The browser setting has to be done on every computer I use to view IP-of-PI/skyaware.
On the other hand, I had to do it only once in script.js and I can view format of my choice on skyaware on all my computers (and even on phone), irrespective of their settings.
You are right, and this is true if this modification is applied to source-code/deb packge.
This will also be true if it is done locally on user’s RPI, but the user has allowed access to others through Internet to view their IP-OF-Pi/skyaware page.
For users like me, who have not given access to others on internet to view their skyaware map, setting locale in their RPI in script.js should not cause a problem, I think so.