LendingLedger.setRewards accepts _fromEpoch and _toEpoch params. The only check that function does is if epoch are set as weeks. It allows to provide epochs that were already set before. In case if this will happen, which is likely not the case as sponsor claimed, then cantoPerBlock will be rewritten for the epoch.
Increase cantoPerBlock for the epoch.
cantoPerBlock[i] += _amountPerBlock;
