Daryll40,
What you are saying is "technically illegal".
UTMA money is a gift to the child.
529 money is owned by the account owner and the child is the beneficary.
If you move UTMA money as you suggest, you are transferring ownership, and although I am not an attourney, I beleive that is illegal. (Joe Hurley please respond).
But what you can do is as bwilk has stated, use the UTMA funds to open a 529 for your child with the beneficary then locked in.
Since you also stated that you would replenish the UTMA account, why not just use the "replenishing" money to open the 529 account? That way you would not have to sell your UTMA investments now, in this market.