No. It is not possible to change what is displayed in the app.
For audio tracks, the Plex LG app displays only the language and audio type. It does not display the track title.
Some other Plex clients such as Plex Web and the Android mobile/TV app can display the audio and embedded subtitle track title. I do not recall seeing a definitive list of which clients can display the audio & embedded subtitle track titles.
You can use MKVToolNix Header Editor to change the track title in MKV files.