I've tried getting my players to learn new positions, and not once have I seen a dropoff in talents
I did see in one league that his stars dropped from 2.5 stars to 1 star and the only change was him going from LF to RF...and he doesn't even have a worse range in RF than he did in LF
I think that ones a fluke, because all his batting and talent ratings are the same as they were before
on a side note...I just got pat burrell to learn 2B by playing him there for 2 weeks