Here's the answer to the questions about what license is required to repair and operate your transmitter. I hold both Ham and Commercial Radio Telephone licenses and neither is required to repair your equipment. You do need a valid Ham license to operate on 50 megahertz (notice the word operate). No license is required for 72 & 75 Mhz. I know there are people who just can't belive this but the following has been copied and pasted from the FCC website for you.
You do NOT need a commercial radio operator license to operate, repair, or maintain any of the following types of stations:
Two-way land mobile radio equipment, such as that used by police and fire departments, taxicabs and truckers, businesses and industries, ambulances and rescue squads, local, state, and federal government agencies.
Personal radio equipment used in the Citizens Band, Radio Control, and General Mobile radio services.
Pay close attention to the statement directly above.
For those that still have problems with this go here:
http://wireless.fcc.gov/commoperators/wncol.html
Now having said this, I wish for you to keep in mind there are requirements to be maintained even though no license is required you can still violate regulations.
For example, you wish to change a transmitter to another channel. Simply replace the crystal with one for the new channel and check the transmitter with both a spectrum analyzer and power output device. Now your set. Don't have these items? Well maybe that's why most people believe licensing and radio shops are required. Not so.