原文Once you announce that you're casting Bolt Bend, no player may take actions until the spell has been paid for. Notably, opponents can't try to change whether you control a creature with power 4 or greater.
原文You don't choose the new target for the spell or ability until Bolt Bend resolves. You must change the target if possible. However, you can't change the target to an illegal target. If there are no legal targets to choose from, the target isn't changed. It doesn't matter if the original target has somehow become illegal itself.