I think OP does not want to do the whole sync process from the beginning.
BitMaxz's solution disables pruned mode only to enable it after deleting blockchain data. OP's node would go back to being a pruned node like it currently is. He won't have to re-download the entire blockchain, but just the size as configured by his pruned node. The syncing shouldn't take long if his pruned node isn't big and he has good hardware and bandwidth.