In my experience and in my area, no one can be "forced" to take a skilled job. A skilled job is different than a particular station/load/work assignment. One of the big problems I have as a steward in my building is that none of the unloaders want to become sort aisle certified (because quite a few want to be able to go home 2 or 3 days a week and they're always short on sorters) so they end up having to pull senior workers from preferred jobs that were previously certified when they have too many call-ins.
Using this issue as an example, none of the unloaders (not even the most junior) can be "forced" to become sort aisle certified but the company can hire sorters directly off the street if no one wants to do the job.
Just as an example: I bid into a preferred job from being a pickoff years ago and went from getting 5.5 hours a day (anything over 5 is OT for a PT in my area) or more to barely 4.0 hours a day. After a few months, I went to the FT sup and asked to be moved back to the outbound and he gave me setup work which kept me content and I ended up staying.
Shouldn't Haz-Mat acceptance auditors, designated responders and international acceptance auditors receive a skilled rate pay for their mandatory training and skills that are necessary to the function of the operation?