Do you want to make the entire relate field read-only or JUST the search field inside the relate field read-only? What is the exact use case that you are facing? I don't see why you would only want to make just the search field read-only. Can you please elaborate?
I want to make the search field inside the relate field read-only. Or please suggest a solution to search filter through search box according to another field value like "Hello Word".
In the record.js in the initialize method you need to set the individual field to have a readonly parameter. For relate fields you need to do the name parameter. This example is for assigned user.
You could use Dependency Actions as they are Extensible and remove the possibility of losing your changes in the record.js file if it is overwritten by another package.
