Is there an overview or systematic study of Sanskrit verbal roots either changing what present-tense stem class they belong to, or moving towards belonging to more than one class? (I am particularly looking for verbs moving into/also taking on forms of Class X, but am also wondering about movement towards thematic formations more generally. So far, my searches haven't had any useful results.)

I was going to go through Whitney to make a list of my own; but before doing that, I thought I'd check whether the kalpataru might have a piece of fruit all ready for me.

Many thanks,

     Antonia