New home. Bathroom tile floor grout was sealed at move-in.

At 12 months, grout repair (cracks from new home settling) was done with the wrong color of grout. Now, the builder is coming back to stain the grout to make it uniform. They plan to use a stain and seal product to, presumably, stain then re-seal the grout. The stain color will be the original grout color, since 2/3 of the floor is that color.

Questions I have:

What is the correct process to insure the stain is absorbed uniformly?

Should the floor be cleaned/prepped in some way to insure the stain is absorbed uniformly?

Do they need to strip the original sealer from the entire floor before applying the new stain and seal product?

Is this a 2 - 3 hour process, or multi-day? Should there be time between clean/prep and staining to allow the grout to dry or better absorb the new stain?

What sort of future issues can we expect?