MC uses a lot of different techniques while using the same base process of changing his had to spectral form, and then inserting them inside other peoples bodies. But no one really asks for more, even if they feel really good because its too much stimulation.
As for MC, he had only used the Age-Reversing process on 2 Ghoul's, one of which we see in this chapter, and the other one should debut in 3-5 chapters.