SWG iRule per-packet policy

You can do it with an iRule. It is not possible use iRules to switch PRPs, but you can create source Ip-based branches within a single per-request policy. In the Per-Request Policy, you can create an Empty action, and assign a branch to it with the following check:

expr { [IP::addr [mcget {session.user.clientip}] equals "10.0.0.0/8"] }

That branch will hit if the IP address comes from 10.0.0.0/8 subnet. There is an IP Subnet Match action the main access policy that is unfortunately not available in Per request access policy - so you need to create it manually.