Might it be possible to modify some protection glass that almost fits?
If for example a speaker hole is not exactly where it should be, is it possibly to use dremel tool or sandpaper to tune it to the right dimensions?

I'm using a shorter glass protector on my Jolla, thus all the needed holes are above it I'll probably do the same on my Jolla C, when it arrives.

The first Jolla C have a screen protection on the display . Whether the next even have it we need to see . Let's see if the next have that also . However, it was a normal film , no Tempered glass or so.

It's better to use a cutter. Of course, before the protection is fitted

To glass?

Please note juiceme was talking about a glass protector. That is, a protector made from glass. Tempered glass, usually.

Yes, exactly. Tempered glass screen protectors.

Or at least that's what they are called in the internetz. I have never seen or held one so am a bit sceptical but from what I have understood they are very thin glass sheets (under 0,1mm?) that are supposed to be very hard and scratch-resistant.

I confess I cannot understand how they are supposed to be handled without breaking, as far as I understand glass is brittle especially when hard.
And I don't know how they attach to device, is it by glue or by electrostatics or what?

I would use a cutter and a revolving punch to make holes. For long holes, use the punch and make 2 round holes and then remove the leftovers in between with the cutter.
Of course this goes for plastic protection, not the glass ones.
https://www.amazon.com/InvisibleShie.../dp/B001S00KNI

Guys, keep calm! when the Jolla C will be out - there will be enough screenprotectors on ebay / amazon. Here in germany there are enough companies, who will make screen protectors, if you send them the correct photos and sizes of the device.
one of them is Bedifol GmbH...

Tampered Glass is a composit of at least 4 layers, much like your car windscreen.
Usually starting with shock absorbent and adhesive silicon on the bottom layer that sticks to the screen, followed by PET film, and an optically clear adhesive to sandwich the previous two layers with the next two, which are the actual hardend "tempered" glass and oleophobic coating to keep dat grease on ya fingaz.
All is compressed to neat 0,4mm thickness.

You do not want to drill or cut because it will completely mess up the structure and planeness.
If Bedifol can offer custom TGPs, they actually have to produce them in small batches. That could be possible but i only saw them customizing TPU and other plastics which they can cut out from dummys.

I am sad to have no glass on the jolla c and bit concerned about the feel of the Jolla C protector.
No bad reports as of now, but i totally prefer my phones naked and touch on bare glass.
All TGP i tried felt like plastic and sticked a little due to the coating...
When i use the n900 its 90% stylus. Still love the N8 glass.
But <rant off>, i think i can cope with a irreplacable protector if it fits perfect and feels at least OKish if i concider the price.

Hang on a minute. A non-stick coating feels... sticky?