I am also having difficulty figuring out "Trim Line Mode" It may be the same as "Assembly Line Mode", though not sure.

It seems to be of a similar category to "transport mode". I somehow put an E39 I was working on (twisted seat repair) in transport mode because I did not let it go to sleep before disconnecting battery.....INPA was unable to deactivate it, but ISTA was able to deactivate it.