My plan is to do a pretty standard search replace, replacing all instances of old_string with new_string. The problem is that I only want to do this for an arbitrary number of old_strings following a specific prefix. So for example:
old_string = "a"
new_string = "b"
prefix = "xxxx"
xxxxaaaaaaaa => xxxxbbbbbbbb
xxxxaaapostfix => xxxxbbbpostfix
xxaaaa => xxaaaa
etc. I'm not sure how to do this. I imagine there's some way to say s/xxxxa*/xxxxb{number of a's}/g or something, but I have no idea what it is.