Well he didn't "fix" it, he hacked it to work for one tenant. And to allow said tenant's non-tenant's friends free access into the building. "fixing it" would be restoring the voice call ability to its original function. Not modding it for one random tenant's Apple Home setup.

And it's definitely possible to get in trouble for "fixing" something if you're not authorized to fix it.

I would call this "bypassing building controls to allow unauthorized access to the building." Frank has access to the building through the allowed means per his lease, not through any means. If his lease is like mine there's a whole page to initial about being granted access through the gates or pool or whatever with only the complex-assigned keys and RFID tags.

(I presume Frank lives in the US, and his state's tenancy laws similar to mine apply.)