Contact the manufacturer of the sealer and ask if they have a product that will remove their sealer, or if you will just have to wait a couple years. They make grout stains to change the color and at the same time applying the stain also seals the surface for practically a lifetime......(they say).
Many brands of grout stain, AquaMix is one that is well known.
Tile 4 You LLC Troy, MI - Consulting by phone/internet -PAYPAL
DITRA Installs - KERDI Watertight-Mold-Free Showers. I have NEVER made a mistake, I thought I did ONCE, but, I was WRONG!A+ BBB rating - est. 1987 - over 50 yrs. exp.