1. When you rename files, the Play button no longer works because the "Movie File 1" field does not change when files get renamed. You have to manually go in and edit every file's "Movie File 1" field to match the new file name to make the Play button work again. 2. Make it so that you can batch edit "Movie File 1" (and other fields for that matter) using expressions.
I have check the function and it should change it.
The only condition because the field is not updated if, after the rename, XMM cannot found the "New" movie file (I mean if the rename has failed, maybe because the movie was blocked by other programs).
In that case you should see an error in the Log Textbox and the filename remain the same as before.