Since you have the pics, I would talk to the places over the phone, send the pic in an email and the dimensions. They will probably ask for outside and inside diameters, etc. Do these come off easily? I know some come off for cleaning purposes, etc. If they do, just take them in. I am guessing that as long as the inside part fits, if it's a little bigger on the outside trim that would be OK. Smaller may show some colour difference on the tub's shell itself.

Are you talking about brushed chrome or nickel. They are two different finishes. Brushed nickel is more popular and easier to find things in. I don't think there is anything wrong with mixing finishes but I prefer to stay in the same color family. We did a mix of metals in our bathroom, chrome (Moen) in the shower, brushed nickel for lighting, towel bars and toilet paper holder. I found sink fixtures with the body in brushed nickel but they have a trim in chrome on them too. For the cabinets the handles I wanted to use only came in worn nickel. Our bathroom leans to the traditional side and the mixture still works beautifully.

If your spidey sense is acting up and you aren't comfortable with what you're seeing, stop him now! I suggest a heart to heart with your contractor. What can be done at this point depends upon what happened, i.e. whether this was something you talked about and agreed to during the design stage, or whether he just started doing it on his own, which would seem a bit odd. But even if you originally agreed to it, if you don't like the way it's turning out, don't let him continue. You might have to pay for him to re-do the part he's already done, but better to do that now and end up with what will make you happy rather than to not speak up, feel totally uncomfortable with the whole thing, and end up hating your beautiful new bathroom! I usually know to follow my gut on stuff like this because our guts are usually more accurate than our heads. :-) You're the boss here. it's YOUR bathroom and you should make sure it's what will make YOU happy! No need to be confrontational or to blame him for it not turning out how you'd hoped. Just a "Hey, we really need to talk about this trim; it's not doing for me what I'd hoped Can we sit down and talk about some options?" Your contractor, if he's a good one, will want you to be happy as much as you want you to be happy. Hope this helps! :-)

Is your tile or other finished wall surface already installed? If not it's easy From my experience With the finished shower walls in place, replacing valves require going in from the back side of the wall. Otherwise you'll need to tear out the installed tile. If you have tile installed and access to the back side it's a matter of opening the drywall and removing the valve from that side. The existing tiled opening for the valve, may not be the correct size for your desired valve and would be a problem and probably require taking out the tile.