IIRC forceLimits 4 means the end user can't change some of the settings that would regulate the morphing while in Poser - it's a way of preventing the end user from messing up, and can only be changed by text editing.

So maybe you could try forceLimits 0.

If you look at various parameters that ARE hidden, like smooth or joint, they all have a keys line reading k 0 0, but I doubt that it's essential to change it. They also have a staticValue line equal to initValue in some cases, and interpStyleLocked 0, which are probably also not essential in this case.