There are a couple of ways in which that could break.
in reply to Re^2: List manipulation headache
in thread List manipulation headache
It will break on lines where the first "wap" is not wap1 (we don't know if that can occur in the file) and it will break on wap11 through wap19, which seem to be valid data (OP: the rest can be abbreviated to 2,3,4,5,12,34).
I seem to remember some regex element that tells perl to do a replacement on the nth occurrence(s) only, which could be used here, but I can't think of it now. Maybe I just made it up.