Hello everyone!

So I have this problem where I am temporarily forced to play on my computer. On this there is only "A Realm Reborn" but none of the addons installed. I would like to do so since sitting around in Limsa isn't too much fun at all. Now here's the question:

Buying the addon key each is about 20 to 35 €. Buying the full game key (ARR, HW, SB) is slightly under 20 €. Obviously I'd much rather pick the cheap route since it's just a temporary solution. I now am worried that if I buy the cheaper complete game key and try to enter that, it will tell me, that ARR is already registered to the account and I can't use the key at all but would have to use single key codes for the addons.

Does anyone have experience with this and can tell me, if I can use the full game key code, or rather not? Any help would be greatly appreciated!