Personally, doing a lot of direct patching to a production system scares me. I worry about introducing bugs/hidden dependencies that wouldn't be represented in source code, and getting conflicts between multiple developers updating the same lisp.
Maybe your button should only allow "load this asdf system". Then every code you use as a patch is a system that can be checked in -- hopefully just the same as you'd have in a fresh image, though sometime you need special magic (unintern, fmakunbound, etc.) to upgrade a live system that you don't need in a dead one.
[ François-René ÐVB Rideau | Reflection&Cybernethics | http://fare.tunes.org ] Grâce à la bureaucratie et au socialisme, il n'y aura bientôt que deux partis en France: ceux qui vivent de l'impôt et ceux qui en meurent. [Because of bureaucracy and socialism, there will soon be only two parties left in France: those who live out of taxes, and those who die out of taxes.] — Achille Tournier, Pensées d'automne