Im not sure on the RST as I've only had it a few weeks but my last car (Fiat coupe 20vt) and my other car (lancia delta integrale) both use EBV's.

These are preset to around 0.6 bar and using a solonoid open to boost to 1 bar when certian conditions are met (revs, foot to the floor etc). When the engine goes into limp home mode or detects any knocking the ebv will close only allowing you 0.6 bar. If you remove this and fit a bleed valve the ecu has no way of reducing the boost should a engine problem occur.