Before

After

I just twisted the spring a little and the plastic just snapped off.

Fuji FP-100C on the left and Polaroid on the right.
It was simple to switch the plastic Fuji backing with the metal Polaroid one. You can easily slide the backing off of the polaroid and slide it on to a Fuji pack but I feel like there is more of a chance to mess things up and its only a temporary fix. I'd suggest breaking or bending the spring because it was so easy and effortless.