Use sRGB for your images. I'm not going to say the costco specific profiles found on the internet are "bad", but....here:
1. When the op shows up from day to day, the chemistry is never quite exactly what it was the day before. Replenishment rates are adjusted to keep it within acceptable limits (probably +/- .1 or .12 for Costco, but I'm not sure).
2. There will be a startup "test print" made in the morning when the lab is first opened. This print is then scanned through a densitometer that is on the printer. The densitometer is occasionally (lol) calibrated with a white/black wedge that is (this never happens lol) safely stored in a pouch. Anyway, after the scan it adjusts the color to be correct (which means "within tolerances"). If it's way way off, one might need to run two or three of these. This of course varies with temps, the paper (what paper did they even use when running the daily setup today, anyhow? Was it 6" luster? probably. maybe?), the chemistry, how worn out the AOMs are, how clean the stabilizer and rollers in the machine are, etc.
3. Most Costcos use a Noritsu wetlab. Some use Fuji. Regardless of which it is, or whatever anyone else tells you, both of those wetlabs are going to ignore any ICC profile present in your images and assume sRGB. I think there are some settings in some newer versions of MS01 that might let you do something other than this, but I'm not sure (I'm not a Fuji or Noritsu tech)--and I know Costco/Fred Meyers/Sam's Club don't have it set up that way.
Get your prints looking how you want it on a reasonably accurate screen (NOT the Costco kiosk screens, they are crappy TN panels...the new Atech monitors are substantially better than the Planar ones, but still they are just a TN panel that goes through NO calibration whatsoever...there isn't even an ICC associated with them, at all) (and no, I don't work for Costco just FYI), and use the sRGB profile. You can try some custom Costco location profiles, but in my opinion this won't produce more accurate results over a long period of time than using sRGB (they might be more pleasing though, and if they are, by all means, use 'em), because the color output varies quite a bit from day to day.
Do note that, in my opinion, if you go get your photos printed at any retailer, Costco is the best place to do it. Imho. They make a TON of money off of photo and treat it very very seriously, and they maintain the machines well.