Yes i know that ED has only given us the option for 2 GBU-12 on the TER9A, due to clearence issues on some loadouts.
But it definitely should be technically possible to install 3 GBU-12 on that rack, and this configuration shouldnt interfere with all loadouts.
In the end its the same discussion as with the tripple mavericks, not recommended doesn't mean not technically possible.
So please ED, let it come to the discretion of the user on what they want to do with their aircraft, no matter if it would be done irl. or not!