I just read through this thread and it compelled me to see how my guitars have held up with humidity changes over the years. We still have the two Strats and one Ric bass. All were built in the relatively stable humidity of my basement back in Chicago and all are now in Florida where the A/C is on all summer and the house is opened up all winter. Today the humidity is 93% with temps in the 70s and it feels sticky inside.
On one of the Strats (curly maple neck with cocobolo fretboard) I cut back the tangs and filled the tang cut in with cocobolo dust and CA glue. No measurable sign of changes due to humidity on that guitar.
The frets on the other Strat (curly maple neck with Macassar ebony fretboard) were filed smooth and I could see the tangs are recessed a bit. The cocobolo has swelled. But the frets are still snug against the fretboard. I don't have an instrument that can accurately read the fretboard swelling but it's too small to measure with a steel ruler that reads to 64ths.
On the bass, which has a laminated maple & Koa neck with a Macassar ebony fretboard, the same thing has occurred as above, with the frets still snug.
I don't know how dry the air would need to be for the frets to protrude but I can see that without humidity control, the fretboard wood could eventually shrink enough to expose the ends of the fretwire. The humidity in my shop back north was around 35% when the guitars were being built, if the dehumidifier reading was accurate.
As for filing down the protruding fretwire, I start with a file and finish with sandpaper glued to a straight edge. But that takes off some wood, too. That's not a problem for a rosewood, ebony or dark wood fretboard glued to a maple neck. But it does present a problem with a solid maple neck in that you will need to finish the newly bared wood and that may mean matching the tone of old lacquer or toned poly. If you don't apply a finish, in time the bare maple will darken with dirt and oil as it is played.
I did a Google search for videos and found some luthiers put tape over the fretboard but I can't see how that would work. If you file down to the tape, once you take the tape off, the frets would protrude the thickness of the tape.
“Travel is fatal to prejudice, bigotry, and narrow-mindedness..." - Mark Twain
Diapers and Politicians need to be changed often... Usually for the same reason.