This comment sums it up pretty much, also depends where the hot and cold water supply connects to the valve behind the tiles you might need to remove more tiles around it or make the cavity for the valve bigger to re-route the pipes. Some concealed valves have the connection points on the sides, some on the bottom, etc. Also they can be different size from the current one. Best case scenario of you can access it from the other side of the wall, that makes things probably a bit easier and less mess in the bathroom.
Good news is once you remove the old valve you can fit pretty much any type of valve: thermostatic or manual mixer depending on what you are looking for.
I would definitely not call it an easy DIY project, but everything is doable.