I want to add some code to pfctl which would add all important rules to pf. In such way, if that rules wouldn't be in pf.conf they would BE in pf.
I think it's a very bad idea. The best you can do i think is to writea pfctl wrapper script in order to load your mandatory rules and rename it to pfctl. Anyway, you would better play with sudo and create and account for you and another for the other admin.
If you persist in that idea take a look at pf(4). cheers, Frangois Visconte