Spheres won't reload libraries already loaded. That's how Gambit works too, you can't reload compiled files. If you want to reload a source file, it is possible but I think changes need to be done. The procedure doing all that is in spheres/gambit/library.scm and it should be easy to change.
I never wanted to reload a module because if you work with the REPL you do all the dynamic development there, and the libraries you load are "stable"
I make an example I'm fixing some stuff in the spheres libraries. And to test the fixes I need the REPL. Each time I must exit from REPL and then enter again. This is not dynamic :) Maybe better to run tests from the shell?