Shouldn't the restriction be placed on the use of the shared resource (the air)? That is, modifying the transceiver should be fine on its own.

What I'm trying to point out is that your comment seems to suggest restricting users from making any (all) modifications, even if they wouldn't affect anyone but themselves, because they might make a modification would affect others. I think one should be allowed to make any modifications as long as they're made responsible for how those modifications affect others. And even if a modification potentially (not through every use) negatively affects others, they should only face consequences when the use actually affected others or went against regulations of the shared resource (the air).

Of course if you buy something, change it and start messing with other peoples lives you are breaking the law. Doesn't really have anything to do with a right to repair.

The obvious flaw in this argument, outside of what others have already mentioned (doing that is independently illegal), is that you don't need to modify an official device to do something like that. Building a radio jammer out of fundamental component parts is not a complicated affair.

It's like arguing that people shouldn't be able to modify their home batteries because they could use them to purposely damage the power grid. That's kind of a ridiculous scenario to worry about when the same infrastructure is already vulnerable to utterly pedestrian physical sabotage. It's a facile rationalization for imposing restrictions that have an ulterior motive.

There's already FCC rules for that sort of thing, it's illegal whether you buy, lease, "license", or even build the transceiver.

I'd say it's fine to modify it to be able to do that, as long as you don't actually turn it on and make it disrupt other people. For example, a car is very capable of crashing into people, but even though it can do that we expect people not to use cars in that way. Even though cars can be dangerous if used irresponsibility, there are legitimate reasons to have cars. Similarly, there are legitimate reasons to modify radios, and we should just expect people to use them responsibly the same way we expect car owners to use their cars responsibly.