That's a great point, Simon. I'm planning to top-mount it -- as you say, less vintage but more convenient. I'll use the white pickguard that came with the kit as a jig.
I tried putting the clear coat on top of the decal; I wanted to see what the effect of brushing it on would be, so I used the brush on the "Made" of "Made in London" to see, while I dabbed the clear on vertically with the same brush on the rest of the decal. The reason why you need to dab the clear on is pretty obvious:
For a second coat, I brushed normally over the now-messed-up "Made" and also over the "in", and then dabbed vertically on the "London" -- you can see that the first coat was sufficient protection, and the brushed "in" looks fine, and the "Made" is no more messed up than it was after the first coat:
So, the next step was to put the decals onto the headstock properly, with the tuners loosely attached so that I could check how it looked:
I'll leave them a couple of days and then carefully dab on a coat (or maybe two) of clear.