I am looking to do the same thing on my Mk7.5 GTI when I get used to the power! Shame, because at the moment they are on sale.
But yes, it will 100% be detectable by VW, even once it is taken off. It is a risk you take for the performance.
The crucial factor really is whether the remap has a toll on the mechanical components of the car over time, or if it this toll is negligible enough to risk your own warranty. (detection of a remap will invalidate your drive train warranty).