IMO for tracks with a certain length of artist + title text, it should stay centered regardless of whether the rating is turned on or off. When the text becomes long, it should then shift to the left to make use of the available space.
That will be a matter of opinion.
Is the center in the middle of available space for the title, or is the center in the middle of the progress bar?
Or is the center between the left side of the progress bar and the left side of the time/duration?
Or should the center be in the middle of the whole MusicBee panel?
This is something that probably many will have different opinions on.
It is also concerning only one of the available display option for the player panel.
Since I am assuming this is not something other users or the developer considers an issue, it will probably be best for you to create a skin that handles this to your personal preference.
You could then place the time/duration, and the rating left and right of the progress bar, and the text would always be centered in the middle of the progress bar.
(or look for skins that are already have such a design)