Combine custom php with Wappler connector

Hi,
Is there a way to add some custom php to a Server Action in the editor?
I have added <?php session_cache_limiter('private');?> on top of one ServerAction and it is working great.
However, this line is overwritten when action steps are modified in the GUI.
Is there any tagline that I can use to indicate to the GUI not to alter my custom line?
Thank you