You can't change the "account designation" because the nephew is the legal account owner now, with a designated custodian (I assume the uncle) managing the account for the nephew's benefit until the nephew reaches the legal age of majority and can take control.
The only special tax rule, as compared to a traditional 529 account, is that the funds can only be used for the nephew's benefit (the beneficiary cannot be changed as can be done with a traditional 529). The five year superfunding of the account can still be done; this has more to do with gift tax law and the annual exclusion amount rules than the type of 529 account (UGMA/custodial vs. traditional).