Different child theme php for Wordpress multi install subsites

Hi,

I have a Wordpress multi install using the same GeneratePress child theme, but the php added in the functions.php file should not be used by all sites. Is there a way to do this? Either in functions.php or by having different child themes? The issue with the last option is the name of the child theme, I presume. If it would be possible to have two child themes witht the same name, there would be no way to distinguish them from one another.

Thank you for your help!
Best regards,
Wim