If you know the exact offsets in the string you want to replace, then substr() is definitely the way to go. Read its documentation, try it out, and post here again if you need further assistance.
Jeff japhy Pinyan,
P.L., P.M., P.O.D, X.S.:
Perl,
regex,
and perlhacker How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart