The answer is yes, but it may be easier and cheaper just to get a new vanity. Or reuse the vanity and put it on a platform.

I did something similar to what I think you're proposing. We had a Corian fabricator make a top with an apron front that spilled over about 6". The 60" top with double sinks was about $2000.

i don’t think extending the water hookups and drain will be an issue.

i would be most concerned with having someone skilled enough to do the work well. if you go with a thick marble countertop, a look i love, it’s my understanding that it’s not one thick slab but there are sides/an apron. so it’s not necessarily a weight problem, but it still needs something to sit on/be applied to.

there will probably be other random issues, like moving outlets to meet code.

I have a 31” H bathroom vanity that I do not want to replace but I prefer to raise the vanity height to 34-36”. Could I replace the countertop and build up the height with a thicker-taller countertop? Such as vanity 31” H and countertop 4” H? What does that do to the plumbing to new sinks - could it be lengthened/extended?

Thank you