I did cut regular shade of the same material with an exacto knife without problem but didn't have to do any altering to my arched one.
It does a fairly good job blocking the light, but it is not a blackout shade.
I would think that is possible. It is only fabric, no metals or heavy materials. It can be cut with a box knife and is easily done. I trimmed mine with no problem.
Yes, it can be altered/cut with scissors to fit.
I have the Arch Window Shade which fits neatly into a perfect half circle arch window. If your window is anything less, you've got some cutting to do. Judging from your dimensions and picture I would make a pattern, open the fan-shade and cut it to pattern. I can't imagine finding anything for your windows unless you have them custom made.
I love my arch shade. I'm not sure that you could paint it but I would say you probably could. It feels like fabric/ paper but holds up very well. I did have to trim mine some, but very simple to do and it looks nice.
i posted before...would not paint these
When shade is opened, it is held to window sill of arched window by two-sided sticky tape that runs along base of opened fan.
Check with Home Depot or the manufacturer. I'm certain that they can accommodate your needs.