Cutting Concrete Block Wall
Yes but you will be miserable, the small blade will not cut through but one side, then you will need to break that out without damaging the countertop. Block is brittle and needs room to remove it. You do not want IT to find the room by raising up the countertop and cracking it. The dust will be tremendous, and getting the blade to cut through to the back side of the block will be a real treat, unless you cut it from the inside and that would doing it blind after the dust starts.

Bite the bullet, rent a gas powered cut saw with diamond blade that has a 6" cut depth. Get pointers from the rental company. Use dust masks, and fans. After the vertical cut is made, make a cut from the edge to separate the top from the bottom. Maybe even 2 cuts a few inches apart, so the top has room to drop down without raising and cracking the top tile. The corners will be the only thing left to detail with your right angle grinder.