Changing number of fiscal periods from 12 to 13

During a support call with a customer yesterday, I saw that he had changed the number of fiscal periods from 12 to 13 for the current year (beginning 4/1/15).  Other than the obvious problem doing year on year comparisons, will this break anything?  We have modified the Inc Stmt and B/S to do "period only" reporting, but no other financial reports are being used.