Since New START counting rules count one bomber as just one warhead, regardless of the actual number of warheads doployed, the U.S. Air Force could already add more warheads to its bomber force now if ordered to do so.
airandspaceforces.com
Air Force Ready to Add Nukes Once Arms Control Treaty Ends
The Air Force is ready to add nuclear warheads to its bombers and missiles if ordered to do so when a key arms control treaty expires.