Flooring Tile - Grout fix

Here be the situation: I'm nearing the end of an ill-conceived project to replace some of the field tiles on my bathroom walls. I replaced the cap tiles on top and the cove tiles at the bottom (to achieve a color change), and tried to leave the 4X4 white tiles that compose the majority of the wall intact. Mixed success on that last aspect...some of them loosened up and some broke while I was beating on the ones that I actually intended to remove. Sooo, what I'm left with is a hodgepodge of new/old tiles, areas that require grout, areas that don't, and areas with 'old' looking grout. What I'd like to do is cover the entire area with 'new' grout, effectively covering the old grout while applying grout to the areas requiring complete grouting.

From reading other posts, I think I need to do some grout removal before I start. My questions are: 1) can I skip the grout removal step by using an epoxy based grout (spectralock), and 2) if I remove grout, how much to take out and what is the best process? My grout lines are 1/16" thick, so grout removal is somewhat difficult. I've (extensively) used the 1/16" dremel tool during the project, and I'm not thrilled at the prospect of using it on all remaining grout lines. I also have a grout saw, but it is too thick for the 1/16" grout line. Does there exist a grout saw that would work for 1/16" grout? Or is there a better way I haven't thought of?

Sorry for the length of this post...and many thanks in advance for any insight you might be able to give me.

Patricia