[Zeke]

FOA, sanded grout is for >1/4" joints. Your question is about removal, so what width joints are we talking about?

I might try an acid wash followed by a neutralizing rinse and smear in new non sanded grout regardless of which you have. If you are bent on removing, just be aware that any rotary tool can go off course and into the tile. So you'd need a guide and a vertical wheel no wider than the joint. I guess that is obvious but I mention it because it will be very difficult to use a rotary tool in 1/8th joints. Most regrout companies weaken with acid and hand remove using hard and soft tools. Or should I say regrout companies use acid on most jobs instead?

Oscillating tools are sometimes used as well and especially handy in corners and hard to reach areas. I will recommend that if you haven't done this to limit your initial work to somewhere that doesn't show or just hire this one out. This is not easy work, far from it. I've done too much for my liking.