The train has already left the station.  No, absent special circumstances, you can't adjust the credit-elect to a lower amount.  Special circumstances would be, for example, death of the taxpayer.  Or maybe just floods and fire or other federally-declared disaster.  It's like getting back an estimated tax payment once the check is cashed.  

Tell your client to stay away from those flaky partnerships and he won't have to worry about amended K-1s.