Change custom font size at run time

No

Damn… so is there no way to create different size version of the same font? Such as small, medium, large? Something like this…

When using bmfont with a ttf file, you specify the height of the font (as well as other things).  I use that to create small, medium, and large versions of a custom font for things like watch faces all the time

Ok understood. So if you are using a font as icon you’re not able to adjust size at run time; you basically have to define everything in advance, haven’t you?

I don't change the size at runtime, just pick which of the 3 sizes I want to use. Large for hh:mm. and maybe medium for date, and small for other things, for example

And there is a ttf file with a number of typical icons, and in that case which of the custom font sizes varies based on the display resolution and I use resource overrides to handle that.

Yes.

On newer watched you might be able to use ttf fonts but I haven't tried yet

You mean scalable/vector fonts?  Not all devices support those even some of the newest ones.. And the fonts are known to the device in advance, and can't be added.