You got it figured out correctly. Power feeds to the switch top and bottom in forward and reversed polarity then the switch just picks which polarity to send to the motor.
Pulling the fuse won't hurt but eventually you may find the power wire shorted permanently and won't be able to move the slide. Is there any way to run a new wire from the fuse box to the switch? At the very less I would carry a spare length of wire that you may need to use to power the slide by jumpering to the switch, in the event that you get that permanent short.
You could try pulling the red wires off the switch and taping them up. There's a very small chance that the switch itself is failing in a way that causes one pin to connect to the red and white on one same side at the same time. This would definitely blow the fuse. Again, very unlikely unless one or more of the pins are loose in the switch housing and can fall into the contact inside.