To get the old hose off, it'll have to be cut off. Once it's cut off, you ARE committed. I'd say it's nearly a sure bet that you (or your mechanic) won't be able to wrangle a new hose on it without taking the pump off. Expect at least a $150 bill for taking the pump off to do the job (if you won't need a new belt tensioner, add about $125 more if you do).
No offense, but if your stuck just trying to loosen the clamps you're probably not a candidate to remove the pump yourself, so I'd get the mechanic and instruct him that you only want to try and remove the clamps, possibly reposition/rotate the hose and put new clamps on it (and get that antifreeze changed). See if that works before proceeding any further.