Clip Turbine Wheel?

I'm looking into getting my 16t turbo rebuilt and maybe having some upgrades done at the same time, such as a billet compressor wheel and switch to angled flange exhaust housing. One turbo rebuilder suggested he could "clip the turbine wheel to a 15 degree for exhaust flow". Is that a good and worthwhile thing to do? Any downside? Average cost for that service?

Thanks for the advice