Magento 2.1 – How to Change Form UI Component

In your module: add this code to your etc/di.xml:

<preference for="Magento\Catalog\Ui\DataProvider\Product\Form\Modifier\CustomOptions"
            type="Cleargo\CustomOption\Ui\DataProvider\Product\Form\Modifier\CustomOptions" />

and then, in your Cleargo\CustomOption\Ui\DataProvider\Product\Form\Modifier

the content is as following:

    <?php

namespace Cleargo\CustomOption\Ui\DataProvider\Product\Form\Modifier;

use Magento\Catalog\Ui\DataProvider\Product\Form\Modifier\CustomOptions as OriginalCustomOptions;
use Magento\Ui\Component\Container;
use Magento\Catalog\Model\Locator\LocatorInterface;
use Magento\Store\Model\StoreManagerInterface;
use Magento\Catalog\Model\ProductOptions\ConfigInterface;
use Magento\Catalog\Model\Config\Source\Product\Options\Price as ProductOptionsPrice;
use Magento\Framework\UrlInterface;
use Magento\Framework\Stdlib\ArrayManager;
use Magento\Ui\Component\Modal;
use Magento\Ui\Component\DynamicRows;
use Magento\Ui\Component\Form\Fieldset;
use Magento\Ui\Component\Form\Field;
use Magento\Ui\Component\Form\Element\Input;
use Magento\Ui\Component\Form\Element\Select;
use Magento\Ui\Component\Form\Element\Checkbox;
use Magento\Ui\Component\Form\Element\ActionDelete;
use Magento\Ui\Component\Form\Element\DataType\Text;
use Magento\Ui\Component\Form\Element\DataType\Media;
use Magento\Ui\Component\Form\Element\DataType\Number;
use Magento\Framework\Locale\CurrencyInterface;

class CustomOptions extends OriginalCustomOptions{
    /**
     * Get config for "Option Type" field
     *
     * @param int $sortOrder
     * @return array
     */

    const FIELD_IMAGE_UPLOAD_NAME = 'image';
    const FIELD_IMAGE_DISPLAY_NAME = 'store_image';
    const FIELD_IMAGE_DELETE_NAME = 'delete_image';

    protected function getSelectTypeGridConfig($sortOrder)
    {
        return [
            'arguments' => [
                'data' => [
                    'config' => [
                        'addButtonLabel' => __('Add Value'),
                        'componentType' => DynamicRows::NAME,
                        'component' => 'Magento_Ui/js/dynamic-rows/dynamic-rows',
                        'additionalClasses' => 'admin__field-wide',
                        'deleteProperty' => static::FIELD_IS_DELETE,
                        'deleteValue' => '1',
                        'renderDefaultRecord' => false,
                        'sortOrder' => $sortOrder,
                    ],
                ],
            ],
            'children' => [
                'record' => [
                    'arguments' => [
                        'data' => [
                            'config' => [
                                'componentType' => Container::NAME,
                                'component' => 'Magento_Ui/js/dynamic-rows/record',
                                'positionProvider' => static::FIELD_SORT_ORDER_NAME,
                                'isTemplate' => true,
                                'is_collection' => true,
                            ],
                        ],
                    ],
                    'children' => [
                        static::FIELD_TITLE_NAME => $this->getTitleFieldConfig(10),
                        static::FIELD_PRICE_NAME => $this->getPriceFieldConfig(20),
                        static::FIELD_PRICE_TYPE_NAME => $this->getPriceTypeFieldConfig(30, ['fit' => true]),
                        static::FIELD_SKU_NAME => $this->getSkuFieldConfig(40),
                        static::FIELD_SORT_ORDER_NAME => $this->getPositionFieldConfig(50),
                        static::FIELD_IMAGE_DELETE_NAME => $this->getIsDeleteImgFieldConfig(60),
                        static::FIELD_IMAGE_DISPLAY_NAME => $this->getImgDisplayConfig(70),
                        static::FIELD_IMAGE_UPLOAD_NAME => $this->getImgConfig(80),
                        static::FIELD_IS_DELETE => $this->getIsDeleteFieldConfig(90)
                    ]
                ]
            ]
        ];
    }


    protected function getImgConfig($sortOrder)
    {
        return [
            'arguments' => [
                'data' => [
                    'config' => [
                        'label' => __('Image Upload'),
                        'componentType' =>  'image',
                        'formElement' => 'fileUploader',
                        'dataScope' => static::FIELD_IMAGE_UPLOAD_NAME,
                        'dataType' => Media::NAME,
                        'sortOrder' => $sortOrder,
                        'validation' => [
                            'required-entry' => false
                        ],
                    ],
                ],
            ],
        ];
    }

    /**
     * Get config for "Required" field
     *
     * @param int $sortOrder
     * @return array
     */
    protected function getIsDeleteImgFieldConfig($sortOrder)
    {
        return [
            'arguments' => [
                'data' => [
                    'config' => [
                        'label' => __('Delete Image'),
                        'componentType' => Field::NAME,
                        'formElement' => Checkbox::NAME,
                        'dataScope' => static::FIELD_IMAGE_DELETE_NAME,
                        'dataType' => Text::NAME,
                        'sortOrder' => $sortOrder,
                        'value' => '0',
                        'valueMap' => [
                            'true' => '1',
                            'false' => '0'
                        ],
                    ],
                ],
            ],
        ];
    }


    protected function getImgDisplayConfig($sortOrder)
    {
        return [
            'arguments' => [
                'data' => [
                    'config' => [
                        'label' => __('Image Path'),
                        'componentType' =>  Field::NAME,
                        'formElement' => Input::NAME,
                        'dataScope' => static::FIELD_IMAGE_DISPLAY_NAME,
                        'dataType' => Text::NAME,
                        'sortOrder' => $sortOrder,
                        'validation' => [
                            'required-entry' => false
                        ],
                    ],
                ],
            ],
        ];
    }

    protected function getCommonContainerConfig($sortOrder)
    {
        $commonContainer = [
            'arguments' => [
                'data' => [
                    'config' => [
                        'componentType' => Container::NAME,
                        'formElement' => Container::NAME,
                        'component' => 'Magento_Ui/js/form/components/group',
                        'breakLine' => false,
                        'showLabel' => false,
                        'additionalClasses' => 'admin__field-group-columns admin__control-group-equal',
                        'sortOrder' => $sortOrder,
                    ],
                ],
            ],
            'children' => [
                static::FIELD_OPTION_ID => $this->getOptionIdFieldConfig(10),
                static::FIELD_TITLE_NAME => $this->getTitleFieldConfig(
                    20,
                    [
                        'arguments' => [
                            'data' => [
                                'config' => [
                                    'label' => __('Option Title'),
                                    'component' => 'Magento_Catalog/component/static-type-input',
                                    'valueUpdate' => 'input',
                                    'imports' => [
                                        'optionId' => '${ $.provider }:${ $.parentScope }.option_id'
                                    ]
                                ],
                            ],
                        ],
                    ]
                ),
                static::FIELD_TYPE_NAME => $this->getTypeFieldConfig(30),
                static::FIELD_IMAGE_UPLOAD_NAME => $this->getImgConfig(60),
                static::FIELD_IMAGE_DISPLAY_NAME => $this->getImgDisplayConfig(55),
                static::FIELD_IMAGE_DELETE_NAME => $this->getIsDeleteImgFieldConfig(50),
                static::FIELD_IS_REQUIRE_NAME => $this->getIsRequireFieldConfig(40)
            ]
        ];

        if ($this->locator->getProduct()->getStoreId()) {
            $useDefaultConfig = [
                'service' => [
                    'template' => 'Magento_Catalog/form/element/helper/custom-option-service',
                ]
            ];
            $titlePath = $this->arrayManager->findPath(static::FIELD_TITLE_NAME, $commonContainer, null)
                . static::META_CONFIG_PATH;
            $commonContainer = $this->arrayManager->merge($titlePath, $commonContainer, $useDefaultConfig);
        }

        return $commonContainer;
    }
}

This code added some new fields in the custom option section.