Why do you need to do this all with regexes? Can you do something like this?

if (/func1/) { s/blah/blah/ }
elsif (/^#define/) { s/yak/yak/ }
else { s/mumble/mumble/ }
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Your examples look like C code. If your requirements are very complex, you may need to use a more advanced parser design -- parsing C with just a regex is not possible.