I bought a radio that can receive 4 ham bands, but only transmit on 2. Can I modify my radio to transmit on these frequencies legally?
Assuming that you're operating in the jurisdiction of the FCC, there should be no legal issue with you modifying your radio and using it to transmit on those two bands providing the following:
- Your modifications comply with good engineering practice, and
- You do not exceed the privileges (power or frequency) of your license
Unlike other radio services in the US, hams get to build, repair, and modify their equipment. Be safe, be careful, and have fun!