Nice! You can definitely improve it. I'm sure it goes without saying, but I would recommend brushing up on CRT safety if you do decide to crack it open.
That said, I've never really considered it, but technically you could retrobrite a monitor without disassembling it. I think the goto is disassembly because often a deep clean is necessary, and many operations put the plastics outside for maximum UV exposure. But I know mine is entirely indoors, because I have giant window. I could probably fit my Macintosh 128k in my bucket, and de-yellow without disassembly. Hmm.
Another step I need to look into though is I've seen some folks suggest adding a UV protection coating (spray). This is apparently a thing that exists for the car nerds. Hmm.
Speaking of de-yellowing, we've made progress. Before and after.
I made the mistake of putting too thin of a peroxide coating at first, but a few days later I put on a thick one, and it greatly improved.
I think mine needs another fresh coat of peroxide. I can still see a faint outline of the previous owners Apple sticker.