References are "project properties" independent of the configuration
(Release/Debug) so they won´t change automatically. But you can add/remove
references programatically using the extensibility model, so you could build
a macro or add-in that switches references when executing it or clicking a
button. I think that even could be done automatically with some event that
notifies a change of configuration or a build. Let me know if you want to
follow that route, but it would be much better to use project references to
debug the library dlls. Also notice that in Release configuration you are
not debugging, so you can skip the IDE and run the app directly and at this
point the app will use as referenced dlls whatever the probing mechanism
finds first (dlls in the same folder, in subfolder, in GAC, etc.). In other
words, the Release configuration is used mostly to build the release version
and little else...