Carpentry and Woodworking - Replacing stair treads and risers

I am planning to replace a staircase that is not accessible from underneath. Some of the hardwood treads and risers are open on the ends and some are in housed stringers. I am planning to pry out the open ones and saw and split the housed ones. Looking at the other set of stairs going to the basement I noticed that the threads and risters are wedged into the slots in the stringer and are glued. Before I start ripping things out I was wondering if it is possible to insert new wedges from the top or do I need to remove drywall from under the stairs and work from the bottom. Any advice would be appreciated.