How to restrict people to edit snippet of script editor webpart in sharepoint 2013?

Move the script to a js file and place the file in a new document library on your site. Break the permissions on the library and allow Edit permissions for your admins. Remove the script editor web part and replace it with a Content Editor web part referencing the js file

Place your script in a document library where only the dev. group has contribute permissions, others have only read permission, and refer that script from the web part. Set read-only permission on the web part page itself. BTW. is it a web part page, a wiki page, publishing page, or application page?