Hello, it is a really useful new samples' feature "Pitch shifting/Time stretching" which was nearly added to the latest versions of MPT, thank you!

It's not new, it has been there for ten years already.
Anyway, this has been asked before. It is mathematically impossible to do perfect pitch shifting and the library that OpenMPT uses does not sound very good and/or is very CPU-intensive (way slower than real-time). It is simply not feasible to offer such a feature as a real-time effect that would be guaranteed to sound good, and more importantly, would sound identical in future versions (we didn't write the code and the algorithm can change in any library update). If you really need something like this, you can try other approximative pitch shifters like the RoVee VST.