Thanks, Matt. I was hoping that you'd respond as someone who actually knows the system. That's the way it worked when I got my Outback. My sales rep looked on their order list and found one in the color I wanted that was still able to be changed, and he just added my accessories to the existing order.
BTW, I live in the greater Detroit area, so not exactly a hotbed for import-brand sales, meaning that I have no practical choice of dealers. After thinking it over, I guess that the only "custom" item that I definitely want installed is the hitch, and if the dealer is open to installing it and waiving or reducing the service labor fees, then there shouldn't be any need for a custom order other than wanting a particular color (Eternal Blue) that isn't one that appears to be commonly stocked.
I went through this when we got our '15 Mazda 3 from this same dealer. I forget the name, but there was a blue color that again was rare. At that time, my sales guy found one on his list that was due in month or two and tagged it for me. Unfortunately, the car was damaged in a rail accident when on the way from the west coast and I ended up getting one in Soul Red that had just come off the truck (turned out to be a better choice anyway). Anyway, I assume that the dealer can do something similar this time.
Perhaps you are thinking of blue reflex? I think if all you are looking for is a tow hitch I would just ask the dealer to install one and be open to an aftermarket option as well, you can probably get an aftermarket installed for close to the price of the factory installed one if you were to order one that way. I think we were getting our hitches installed for about $350-$400 when I was at my last dealership, but down here in Florida.
We don't have a dealer in the Detroit area, but here is what I would recommend if you are ready to roll - shop your local dealers, but also reach out to out of market dealers. Some of the best deals we've found are with dealers in lower population markets, they have less local population and may be more willing to just move a car for the sake of a sale despite the loss of future service from you. I do believe in having a good local dealer relationship, so if prices are comparable I would lean towards supporting local to you as you may want that relationship through your servicing experience.
Not including dealer fees, Mazda marks up their cars about 2.5-3.5% from invoice to MSRP and holdback is 1% of pre-destination MSRP. So generally speaking you want to shoot for a minimum of 4-5% off MSRP which should be attainable. Now weigh in dealer fees on top of this, if theres a reasonable doc fee of say $500 then 4-5% is a good target, but if they are hitting you with $500 plus $1200 in dealer addendums or some other combination of inflated non gov't fees, then you want to push for a higher discount to offset this. Now an excellent deal is if you can score closer to an employee price which is 4% below invoice, so if you can get in the 6%-8% off territory, you are getting an extraordinary deal.
Lastly, when you are ready to put your money where your mouth is, literally, then time to search for your exact car you want around a 250-500 mile radius from you (depending how many dealers that captures) and try to find an email to the sales manager, draft a polite but forward email stating your interest to buy the specific Stock# vehicle, exactly how you would like to purchase it (cash, finance, lease) with the terms you expect, the discount you would like (perhaps shoot for something like 8% off MSRP - note; not including incentives, those come off on top if available), your zip code and if you have loyalty or active military in your household. Let them know that if they meet those terms that you are prepared to give them a deposit today to secure the vehicle and the deal and come in and finalize.
If the best deals are from a long distance, I would include intent to ship the vehicle to you and ask if this is something they would be okay with up front. If you need assistance shipping a vehicle, feel free to DM me, we move cars nationwide regularly. Good luck!
Also, if you really have trouble finding a dealer to play ball, let me know, we can always ship a car out to you from my dealer in FL, not unheard of for us but economics might start breaking due to the added cost. Ultimately depends on how good or bad the deals are you are able to secure locally.