Muzz. I'm not sure if I'm understanding you correctly. Are you worried that if you tape off the rosewood fretboard (and edges) and stain the maple neck black you are worried about the stain leeching under the tape and bleeding into the rosewood fretboard?

I think thats what you are saying.

I agree that you should go balls out with the black rather than the natural finish because I agree with your style.

If it were me, I would polish the edge of the rosewood fretboard up to 2000, tape it off and stain the maple neck. given the density of the rosewood and with some polishing I doubt it would bleed, but you can't be 100% certain. you could check under the tape after each stain coat and if there was bleed you could try and blot it with a wet rag or if dried sand it back.

I'd probably be more worried about trying to match the maple neck with the body as one black.

Edit: I like the burst you got going on there!