Magento – Magento 1.9 : How to Edit the price of all products؟

Hi Magento provide an attribute by below code

$product->setAttributeCode($newValue)
$ProductObject->getResource()->saveAttribute($product, 'attribute_Code');

Example:

$product=Mage::getModel('catalog/product')->load($id);
$product->setSpecialFromDate('2010-10-28');
// below code use for time format 
$product->setSpecialFromDateIsFormated(true);
$product->getResource()->saveAttribute($product, 'special_from_date');

Using Product Collection:

$productIds = array(1,3,2);
$products = Mage::getModel('catalog/product')->getCollection()
->addAttributeToFilter('entity_id', array('in' => $productIds));

foreach($products as $product)
{
    $product->setSpecialFromDate('2010-10-28');
    // below code use for time format 
    $product->setSpecialFromDateIsFormated(true);
    $product->getResource()->saveAttribute($product, 'special_from_date');


}

The problem is that Magento assumes that discounts are always decreasing the price and to change this behaviour you would have to make modifications to several core files (or use proper overrides).

A practical solution to your situation would be to set the highest possible price (i.e. 120 €) as product price and use price rules to make it cheaper for everybody except those in your 120% group.