I had to setup a bunch of port forwards last week, and like most of the ones I do they required Advanced mode. It drove me crazy to have to switch to Advanced Mode every single time, and accept the warning every single time.
How about one of two solutions:
1) Once the user switches to Advanced Mode in port forwarding for one rule, just default to Advanced Mode for all future rules (at least during that session). Maybe have a checkbox for it.
-OR-
2) If the user has switched the overall Networking configuration to Advanced already, then just assume the port forwards are going to be in Advanced Mode too and don't bother about it any more.