Oh, I see. The debug tool in the instructions has one line that was never updated.
Code:
if pkmn.egg? || pkmn.shadowPokemon? || !pkmn.dynamaxAble?
Should instead be:
Code:
if pkmn.egg? || pkmn.shadowPokemon? || (!pkmn.dynamaxAble? && !pkmn.isSpecies?(:ETERNATUS))
This allows for Eternatus to have its Dynamax values edited (but not Zacian/Zamazenta).
And yeah, you can use any event or anything really to do this. Just use the method
giveGMaxFactor on a Pokemon to give it G-Max Factor. This will ignore any restrictions that would normally prevent this. Note however that G-Max Factor will never display on Zacian/Zamazenta even when given this way (they will still have it, it just won't be visible).