In mid 1979 I bought my first TRS-80 computer ... It was a rom patch that ... also brought on new features like the First Lowercase capability on a home computer.
'79-ish TRS-80 would have also required an extra RAM and a bit of wiring; RS skimped and left out a bit.
I still have my technical manual where I've penciled the circuit into the schematics. Never managed to get it done, though; the RS in Roosevelt, UT in the early '80s sucked something awful. 'Sides which, it wasn't even my TRS-80 to begin with...
It did require extra RAM, about an extra 4k of Static Ram if I remember right. The video ram was in sockets and you pulled out the old ram and installed our new ram which was 2 ram chips piggybacked with an extra Chip Select line coming off the top stack which had to be connected to a tiny bit of extra chip select logic. We managed to create a kit that worked well for people. We also had a service where you could send in your TRS unit and we would upgrade it for you :)