I have taken that switch apart, it can be done carefully so you don't break off the plastic tabs that are around the edge, however, when putting it back together, you will have to use some light glue on the tabs so it doesn't come apart.
The biggest problem with that switch is the slider inside that directs the vacuum, it originally had some type of grease on it to seal the ports when it moved. Over the years, it dries out and doesn't seal. You can clean it and regrease with white grease and get it working again, as I did with one of mine.
If you manage to find an NOS one, they are priced over the moon!!! I was fortunate to find another complete control that had the switch and good knobs and used it to rebuild my original and the switch I took apart and repaired is now my spare.
To replace the knobs, as flypaper said, you can remove the entire arm and replace it with on that has good knobs. Just a note, for those that have heater only control, you cannot remove just the arms, you have to remove the knobs to get the arms off.