[targafarian]

> not implement low-level radio protocols

You don't have to re-implement protocols to commit FCC (or pick your local reg agency) no-no's. See e.g. discussion by this HAM radio operator on his blog (doing legal things, but you can easily do this for non-legal things):

https://yo3iiu.ro/blog/?p=1301

[varispeed]

Even if you don't write custom RF code, you still need to go through certification, so it does not really matter if user can or cannot write their own custom code. It may be just a bit more expensive to get it certified if you make a mistake.

[zozbot234]

That blog post is describing hardware-specific configuration tweaks. It's quite possible for firmware to check that these are regulation-compliant, and good quality hardware will typically do this.