Good position changes are few these days. Some that have worked for me are Rb to TE or WR. Wr to TE will give you pretty good receiving TE but usually poor blocking one. I am only happy with a switch if the new positions numbers are better than I could have recruited that position for and I also want a WE increase. The WE increase usually only happens if you have very few of the new position on the squad.
For ex. I have a rb Im gonna convert to wr and I only have 1 wr on squad. The rb WE will go up. But if I have 4 WR on squad than rb WE will go down.