What do you mean overspent? What is your current favor magnitde and problematic blessing tier? Before you reset blessing as advised above try push in freeplay to gain that favor again. In 99,9% cases if your accout had power to gain certain amount of favor you can gain it again with some effort. At least with some iLVLs and leveled modron core you can go to LVLs 1000+ in one event freeplay starting with 0 favor.
The only overspent favor case could be situation you have spent favor gained due to events/trials additions, but iIMHO it's still better gain some more power due to unlocked blessings and push in freeplay to gain that favor again. Specific situation with e100+ favor when you can not gain more favor in freeplays and only due to events/trials additions is not the case as most expensive blessing cost AFAIR e46 favor.