apply a patch to a complete meta-xxx - before using it (in kas)?

I need a version of a meta-xxx repo that has new syntax ":" instead of
"_". Some other minor things have to be changed too (as compatibility
string)

I check that meta-xxx out by help of kas tool.
Do I have a chance to apply a patch right there once the meta-xxx has
been cloned? The kas docu confuses me a lot.
Guess I can't do it in Yocto, as my first bitbake command it will
complain about the syntax, so I can't "repair" that inside yocto.
Or am I wrong?

Best regards