Yes, that's the one that talks about a transparent image overlay;
the other main thread goes into detail about changing values in a
mce file, but I think it's for n9/harmattan, and not n900/fremantle.
If that's correct, inking the bare surface may be a bad idea. I thought
the digitizer might be under, or even melted into, glass.
It is - "melted" into plastic/glassy thing. You won't damage it by inking the surface, it just sound a little... Harsh, for a surface, that you can't replace without replacing whole digitizer.