Both teams can agree to mutually terminate a contract with no cap penalty (Lukas Krajicek in Philly last year, Jon Sim and Andrew Peters among others this year). Can't see Redden giving up that much money (there's no buyout on $125 waivers) though. Rangers can hope all the want, but it ain't happening.
As for Gomez, no, you cannot change or re-negotiate contracts. If you buy out/release a player, said player cannot re-sign for a full calendar year after. So the scenario you've proposed, though desirable, is illegal.