This link states: "One final, essential note: There is no post-June 1 designation for trades. A team can wait until after June 1 to process a trade and will see the same cap benefits we outlined, but they cannot trade a player in April and designate the deal as a post-June 1 trade."
That would mean Carr's $30 million salary would still be fully guaranteed if we got beyond March 15th and he could rescind his no trade clause at any time. That is definitely not worth the risk.