Originally Posted by Bob Barker

Alright, let's get back to the OP original question:

I wanted to do this last year because I could pick up some 8s bar-ends at a good price, so I asked an LBS mechanic that I trust. Here's what he told me:

You can swap 9 and 10 speed back and forth by changing the indexing gear. You can not do this with the 8 speed shifters. So I ended up buying new 10s.

YMMV