I am running a custom ROM (2.4.5 Green ROM) along with a theme. I would like to grab the 2.3.20 OTA update, as I've heard there are improvements in battery life and signal quality, due to the new baseband and kernel.

If I restore back to stock and update for the new baseband, will all my existing ROMs and backups(via ROM Manager) be worthless? Ideally I would like get the updated baseband and then go back to my current setup (2.4.5 Green ROM with a theme).