Well, generally perlmonks isn't a code-writing service, but since this is rather trivial, here is the one-liner you could use:

perl -pi'.orig' -e 's/^radiusFramedAddress:\s* ([\d\.]*)/changeType: m
+odify\nreplace: radiusFramedAddress\nradiusFramedAddress: $1\/32/' us
+ers.txt
[download]

It uses a regular expression (regexp) to substitute every line beginning with 'radiusFr...' with the three lines ou want. $1 inserts the ip-adress captured in the pattern through the ()

Just execute this on a command line (as one single line wihtout the '+' chars) and you are finished. The original file is replaced and changed, the old contents is in users.txt.orig. Tested it on linux. If you are on windows, it should work too, but I can't guarantee (but there shouldn't be anything catastrophic happening)