How to use script to always open images in a specific Photoshop version within InDesign?

How about using BridgeTalk?
Please refer to this.

Open image in Photoshop right after placing

I don't have Photoshop installed, so I can't test it, but for example:
Open InDesign 21 from InDesign 20 and display the message.

var bt = new BridgeTalk();
bt.target = 'indesign-21';
bt.body = 'alert("Hello")';
bt.send();

I haven't specified the #targetengine, but it works for now. I'm not entirely sure about this part.

Loosely related is this:

https://github.com/vamitul/id-launcher

You can set Adobe Bridge (Preferences > Filetype Associations) to open the specific version you wish to use. Thereafter, a double-click in Bridge opens in the version you told it, while the Finder/Explorer window double-click would open in the current version.