Right now, you can do it in two ways:
- Don't have the Arch key at all. supac will silently skip it.
- You can write a small wrapper in package.nu that checks the presence of your preferred arch package manager in $env.PATH, if it's there then it'll insert the key and value, and not otherwise.
I'd mostly go with 1 unless you're sharing your non-arch config with an arch config on two separate machines.