Entering Fortified stance will result in -50% magic and thief operation effectiveness and gains. This kicks in immediately for the fortified kingdom and slides in over 24 hours for the rest.
this makes it sound like a KD opping out of fortified into full fortified would have a -50% mod and a -50% mod. Assuming multiply them. = -75% effectivness and gains
It could be that fortified gives -50% offensive and defensive TPA in which case double fort would result in no gains penalty? But then opping into fort should be really easy but give -50% gains? I am guessing this may be issue? Uncertain! Too lazy to test!