Magento – Get Category Display Mode

You can create a new yes/no attribute for the category names 'Show block below grid' with code block_below_grid. See here how (or search the web - this is common)
Now edit app/design/frontend/{interface}/{theme}/catalog/category/view.phtml and replace this :

<?php elseif($this->isMixedMode()): ?>
    <?php echo $this->getCmsBlockHtml() ?>
    <?php echo $this->getProductListHtml() ?>

with this:

<?php elseif($this->isMixedMode()): ?>
    <?php if ($_category->getBlockBelowGrid()) : ?>
        <?php echo $this->getProductListHtml() ?>
        <?php echo $this->getCmsBlockHtml() ?>
    <?php else : ?>
        <?php echo $this->getCmsBlockHtml() ?>
        <?php echo $this->getProductListHtml() ?>
    <?php endif;?>

Add a static block into a static block:

{{block type="cms/block" block_id="your_second_block_id"}}