There's no simple/built-in way to apply a regexp to change paths, but it should be possible with a bit of VBScript glue to make it work.
A bit more info on what the regexp needs to do is needed, though.
Is the starting directory name always going to contain literally two characters? If not, what do you want the regexp to do?
How many starting paths are there? If there are only a few, and they don't change, then there is a much easier way to do this which doesn't require regexps or VBScript.
Are you still using Opus 9 as per your profile, or Opus 10 now?
mmm yes maybe if I run a command with the {sourcepath} as argument I can manage the character strings replacement but I'm not sure this is the simpliest way. In addition I don't wan to use external code to DO.
I read that I can't pass an argument to a vbscript code in a custom button. Is that true?
You can't use @script except with the Rename command / rename scripts. (Not officially, anyway. It might work to some degree but it's by accident rather than design.)
You can either put the VBScript into a .vbs file and call that from the button like you'd call a program (i.e. like calling an .exe), or you can use the rename script method I linked to above. ("Abusing rename scripts")