I am a fabricator. if the seam is silicone caulk (it'll be soft) you can just cut thru the adhesive with a "Stanley" knife or equivalent. You may also need to cut the joint between the horizontal piece and the splash. If it's epoxy the easiest way is to saw it out but you'll need a diamond blade and someone handy with a circular saw. You'll also want to trickle water on the saw blade while it's cutting to keep the dust down and have a vacuum hose at the cutting point to suck the dust. Do not try to bust it out; you could easily break the stone on the wrong side of the epoxied joint. Easiest for you is to get a fabricator.

You need to trace where the pipe comes from, in order not to abandon a live water line behind the wall. You’d want to cap that somewhere accessible. Just like a live electrical line. You don’t want damaging surprises there. Can you get to the plumbing from the back side by removing drywall there? If not, removing it is a bigger deal than you think. You’d have to open up the splash enough to cut it back. And thsts aftet the line is capped at the origin in an accessible spot.

I wouldnt touch it without a waiver that acknowledges the hgh potential for damaging the cabinets if they are not removed. The granite is likely to break as well. No stone fabricator is going to want to template with the cabinets in place, or use the old piece as a pattern. Houses shift, and walls and cabinets move. Stone constricts some of that movement, until it is removed. “Exact same sized” things do not go back in the same place, as that shape changes when things are removed.

My focus, for now - since you are planning a full remodel down the road - would be to reduce all of the "busy" and ornate elements as much as possible and make the whole more cohesive. Having the cabinets painted and the backsplash removed and replaced (without moving or harming the granite, which makes both more difficult) will cost a fair amount. If that isn't a worry, fine. If you intend to do anything yourself, it will pay off to seek out education on how to do it without ending up with unhappy results. Painting the backsplash tile a single, solid color could be an option if you decide that you can't move forward with removal/replacement. When you have the cabs painted, you can fill the holes of the removed pulls and then install pulls that match the dark cabinets.