To remove the belt, you either need to pull up hard on the belt to pull the belt into the secondary, or turn the movable sheave counter clockwise and push away to open the secondary. That should give you enough slack to remove the belt. When the belt goes down into the secondary, I use a piece of old belt and jamb that into the secondary to keep the sheaves open. That way, I don't have to twist and push twice!
In the older Polaris secondaries, you will need to disassemble the secondary and add a shim to increase the distance between the fixed and movable sheave. That will increase belt deflection and should stop the squealing.
I would also check the primary for build-up of rubber residue. If there's a black ring low in the primary, it's possible the belt is grabbing the rubber and sqealing instead of slipping against a clean clutch surface. If there's a rubber ring, clean that out and see if it helps.