Hello, I'm porting an Amstrad CPC game to TIC-80 and I also had to adapt the resolution. The original game is on 160x200, compared to the 240x136 in TIC-80 so I had to change the sprites a bit but not that much: it's a tile game (some sort of sokoban-style). The Amstrad CPC possible resolutions are 160x200, 320x200 and 640x200 (the higher the res is, less colors are available) so not all games can be adapted to TIC-80, but sometimes the "useful" screen is only a small subset of the actual screen, you can use that to fit TIC-80 resolution. Good luck with your project!
Yes, you could always use a viewport (clipping region) if the resolution is lower than TIC's - for example, my game for the last Low Rez jam was 64x64 (https://paul59.itch.io/crowd-sauce)
EDIT: Wish I still had my CPC464! :D