You can do it like this:
<?php
$blog_id = get_current_blog_id();
if ( 1 == $blog_id ) {
?>
<!-- Your FIRST code block here -->
<?php } else { ?>
<!-- Your SECOND code block here -->
<?php } ?>
Here’s the whole prettified version of the code you can use (totally UNTESTED, but should work unless there are any silly mistakes that I didn’t notice):
<?php
$blog_id = get_current_blog_id();
$drabello_video_embed_popup = get_post_meta( $post->ID, 'videoembed_videopopup', true );
$drabello_custom_link = get_post_meta( $post->ID, 'links_link_custom', true );
if ( '' !== get_the_post_thumbnail( 'progression-thumb-retina' ) ) {
if ( 1 == $blog_id ) {
if( $drabello_video_embed_popup ) {
echo '<a href="'. $drabello_video_embed_popup .'" class="hover-gradient video-pop-up" target="_blank" rel="prettyPhoto">'. the_post_thumbnail( 'progression-thumb-retina' ) .'</a>';
} elseif ( $drabello_custom_link ) {
echo '<a href="'. $drabello_custom_link .'" class="hover-gradient" target="_blank">'. the_post_thumbnail( 'progression-thumb-retina' ) .'</a>';
} else {
echo '<a href="'. the_permalink() .'" class="hover-gradient" target="_blank">'. the_post_thumbnail( 'progression-thumb-retina' ) .'</a>';
}
} else {
if ( $drabello_custom_link ) {
echo '<a href="'. $drabello_custom_link .'" class="hover-gradient">'. the_post_thumbnail( 'progression-thumb-retina' ) .'</a>';
} elseif( $drabello_video_embed_popup ) {
echo '<a href="'. $drabello_video_embed_popup .'" class="hover-gradient video-pop-up">'. the_post_thumbnail( 'progression-thumb-retina' ) .'</a>';
}
}
}
?>