With the re-crowning of Dora I had to do it twice, because the first time I used s crowning file, and ended up making some frets lower.
It's important to have an appropriately sized crowning file for the given fret size, or this can happen. There is another member that posted about this very issue just the other day.
Also worth noting that achieving a proper crown on a fret is not always done so by only running the file directly over the centre line of the fret. Sometimes the file needs to be run off centre. It's all about how the groove of the crowning file mates with the size and shape of the fret wire.
There are that many different fret wire sizes and specs that it would be near impossible to make a crowning file that fit every one exactly. So compensations have to be made.

I gotta say, even using a dremmel... fretwork is *very*tedious!
Like most things, it becomes less tedious the more you do it. You find easier and quicker ways of doing things as you go along.
My first level, crown and dress took me about 4-1/2 hours. Now I do it in about 1-1/2 (depending on coffee breaks!). I can pretty much do a full refret, level, crown and dress in the original 4-1/2 hours.

I’ll tape the fretboard up before using the crowning file (getting a good one is the secret here, and it took me a while to get one that just worked fast and easily), which generally is enough to protect the board from the file edges. Replace the masking tape if the file is cutting through.
I have taken to just using two strips of painters tape on either side of the fret I'm crowning, and just moving them as I work up the fretboard. I'll replace the tape if it starts to get worn out or lose its stick.

I also agree with Simon that finding the tool that works for you is a huge part of getting your best result. Unfortunately it requires buying & trying to find it, but this has the side benefit of adding more "weapons" to your arsenal. I have files that aren't necessarily my favourite, but still come in handy for certain jobs.