Worth trying. If people remember the story I had entered on a mission to develop a narrower grip for my overhead squats because of my wrist problems when using a traditional wide or "snatch" grip (note the snatch is a lift not a grip). There is just no getting around the pain it cause my wrists to be torqued and weighted that way but there are two main functions for the wide grip in the Overhead squat (as opposed to the Snatch):
1. It is easier from a mobility standpoint. The wider your grip the easier it is to extend the back and keep the bar in the pocket WITHOUT simply stretching the shoulders back with the "reach back" which is a frequent mis-teaching for the OH squat.
2. It helps stabilize the bar laterally.
However, a narrower grip will allow most to eventually support more weight, both from a pure shoulder strength perspective and from a wrist perspective if they have problems with that.
The only way to develop this narrower grip if you are not already blessed with this kind of mobility is to do mobility drills and slowly bring the grip in narrower and narrower, which is what Pity is talking about and the purpose of this prone foam roller stretch he just linked. And I do think of that as a stretch rather than a mobility exercise.
Note that neither of us is talking about stretching the shoulders back. If you watch the video you will see that all the extension is in the back. I personally find prone drills such as these much less useful than the type of drills I outlined in tweaking the overhead squat but we don't need to limit ourselves and it's another tool in the toolbox.
On the internal rotator stretching I want to say that you do not just go working on internal rotation range of motion for the hell of it. Only when there is a marked deficit and this should be a comparison of one shoulder to the other. Also, the idea that the "fascia" stretches real tight being an indicator of the need for a particular stretch is a bit subjective.
I'd try the foam roller thoracic extension with a bar but for the rest I wouldn't recommend it.