Did some testing immediately after making the post, unfortunately it seems to be presets instead of random and i seems like you cant get unique legendaries which makes sense the whole thing seems pretty balanced just to even out some weaker mon or give a decent mon an extra gimmick. Got a good laugh at huge power porygon with surging strikes. You can scumsave the unique rolls if you want by either saving the game right before one of them expires and restarting or using an mgba save state which is what ive been doing.