I assume you mean "setup code" not "device code". A setup code is a device type together with a 4-digit number.

Pick any setup code that doesn't match some built-in setup code that YOU want to use. It doesn't matter whether it matches no builty-in code at all or whether it matches some built-in code you don't want to use.

If it matches a built-in setup code you decide to use later then you'll need a new .wav file to replace the upgrades with a set that doesn't include that setup code, so the built-in one will be accesable again.