Hi,
is it possible to add regex checks to custom profile fields? Just like the checker for a valid username, password, ..
No but you could do this with a plugin
What exactly are you trying to check for?
F. ex. ([A-Z]{1,1})[a-z]{2,9}+_([A-Z]{1,1})[a-z]{2,12} for custom profile field #5, but I'd love to customize a few of them.