I assume the "lacquer finish" is clear. Could it be black (or the wood stained black) instead?

The walking stick appears to be stained/lacquered/varnished/Minwax-ed a medium brown with the wood grain visible through the finish. I'm not sure if there's an option for colors on the product description page. I don't see why you couldn't "do-it-yourself" a different color over the "factory paint". Perhaps a dark stain which still preserves the wood grain pattern visible through the finish?

Does it have the option to change the tip?

There was no option to change it. You can remove it and replace it. Anything other than a push on tip may require modification to the stick

I know it breaks down into 3 pieces but is it the same 3 pieces from a singular staff or "frankensteined" together from multiple different pieces?

It is 3 pieces from a single staff.

what size replacement rubber tips should I order

Hi! I bought mine just recently, so I have never had the need of a new rubber tip, but I measure what I have and the bottom part is 1 inch 1/2, and the height is 1 inch 5/8 and the opening where the stick goes is about 1 inch 1/8. Have you tried to call Brazos company? I think they would be able to tell you better. Hope this help you a little.