So the pogos are usually quite rigid until a jam occurs.... is that correct?
Yes, although I've never actually tried to extend/compress one during a PCU change, so I can't give you an idea of the force involved.
I think if it were such an issue (the scenario you raise) that Boeing would have placed a telltale mechanism on the pogo's such as shear rivets. What was interesting is that the IPC states that certain part number pogo's are subject to corrosion from de-icing fluids. So maybe the opposite is more of an issue, i.e the pogo's not breaking out. We don't use alot of de-icing fluid in Oz so I doubt I'll ever see this issue either.