OK, so I followed Floob’s video and created “startrek.zip.cfg” in the rompath. The file only contains two lines: video_allow_rotate = “true” and video_rotation = “1”.
This config file does not work in lr-mame2010, but works as expected in lr-mame2003. Unfortunately, lr-mame2003 does not emulate the sound in startrek.zip, so this is not a solution for me.
startrek.zip runs in the proper orientation in lr-mame2003 (as in, doesn’t need a custom config), but there is no sound. If I run the game in lr-mame2003 using startrek.zip.cfg, the game is rotated counterclockwise 90 degrees.
In other words, the config file works as expected in lr-mame2003, but not in lr-mame2010, so I suspect this is a bug in lr-mame2010 (or at least the build I am using).
In the meantime, I am able to manually rotate star trek when I want to play it.