My wife doesn't like the looks of the engineered floor our contractor just laid. It's got very little veneer layer (1/16th)and I assume a typical aluminum oxide fortified wear layer. It would look great with a whitewash but how to get adherence on that wear layer? Another professional suggested I abrade it and use another coat of finish, like Traffic HD, with a tint. Any comments on whether this is the best way, and if so, how best to abrade it? Thanks.

Some pre-finished floors have a very tough finish that is difficult to scuff enough for another coat of finish to adhere. There is a system from Basic Coatings that uses a special adhesion enhancer, called Tykote, spread on the floor after a thorough cleaning as the basis for subsequent coats of finish. You can add color to each coat of finish.
You could also try a new abrasive that has diamonds which may scratch the surface enough for adhesion. I don't know the brand that makes this.
It's a "one chance to make it look good type of coating" when you add pigments to the coat of finish. If it doesn't come out good, you can always add another coat, if you think it could look better, though.

That is a really excellent suggestion, I watched their youtube videos and it looks like an ideal solution. I'm going to contact them to see if there's a contractor near San Diego who's experienced with their method. I'll post the result to this site. Thank you!