The TT is very sensitive in that aspect. The MkI had no spoiler, as a result there was 1 killed and a lot of injuries in Germany, because of the instability of the car (rear too light, very dangerous in a corner even with AWD). Audi had to recall the car and add a spoiler.

It has roughly the same rear shape as a Porsche 911 (who happens to have a spoiler also).

So I would not touch it unless it's a spoiler specificly designed for the TT, and from a renowned tuner. If it is they surely have your solution.

(BTW, stay cool!)