I don't see the principle being unscrupulous - no more so than moving mods from one team to another for galactic war. Dead men's boots seems to be pretty common theme on battle fields, at least in RPGs, and probably in real life. (Recycling. Just like the ravens.).
The simplest way to implement it would be to apply power when you deploy the unit, so that is probably what they did.
Getting a mod to level 15 costs approx 100 times removal cost. Assuming you had mods enough for half your characters, and did one swap per phase, that would be 5 swaps per territory battle, or after 20 battles (about 5 months) you would have spent enough credits on swapping to have fully upgraded as many mods as you had been swapping around. (Obviously if you use fewer mods, you will have to do swaps at a higher rate, and it won't take as long.)
Since most of the benefit (2/3 of GP, and full secondaries) comes by getting to level 12 on a mod, which costs about 1/3 of full upgrade price, you would have been able to upgrade a bunch of mods to get most of the benefit after a month and a half.
GP benefit and mod update costs taken from spreadsheet in this thread:
https://forums.galaxy-of-heroes.starwars.ea.com/discussion/127995/galactic-power-value-per-credit-mods-vs-character-levels/p1