This question of Dry Creek profiles (printing to CostCo?) has come up a number of times.
Most printing labs accept RGB files in a standard RGB colourspace only. They may make a printer profile available for soft-proofing purposes, but this is purely so that users can compensate and adjust their image using a softproof preview, until it looks as they want despite the softproof's alterations. Then this specially adjusted and compensated image version - this is, for the typical lab - is saved out with a standard colourspace and uploaded. Often this has to be in sRGB, but not always - could be AdobeRGB, for example.
The Costco options are AFAIK that you can either use a standard service which expects an sRGB file. Or you can use a special service where not only is their supplied printer profile used for softproofing, but furthermore, the image needs to have been itself converted to a non-standard colourspace based on this profile.
In other words, in this workflow an image version is pre-processed by the user specifically for that particular model of printer, and the "no adjustments" option selected on the order form dictates that such a file should be used directly in the print shop, without any intervention or conversion.
According to their instructions (which were not very recent when I last looked into this, so may no longer apply exactly) even tagging this special image version for the print profile used, is not a good idea. While it is possible to add and select a non-standard colourspace working from LR, I don't think it is possible to tell LR not to tag the image accordingly. This rather odd stipulation applied only to poster size printing IIRC.
It is always best to seek specific advice from the printing company concerned.
