Filtering before rendering blocks in edit screeen

I’m using this plugin but I have a filter on my content and I want that filter applied when the block renders in the edit screen. Right now I do it by, at the the bottom of the render_block_template function in php/Blocks/Loader.php where it says:

return ob_get_clean();

I replaced it with:

$output = ob_get_clean();
$output = str_replace("apple","banana",$output);
return $output;

This works fine except that when the plugin gets updated, I have to add it again. Is there a better way to do it?