Javascript field override?

Is there a technique you recommend, where as you can override the JavaScript code for a particular field..and still keep that field type a part of a group repeat?

I was looking at the JavaScript code in the chrome debugger this morning, since the JavaScript code to replace the row titles, suddenly stopped working. Along the way, I looked at the code for the image preview and it occurred to me, I could get what I wanted with the image preview using a field override. Is there a proper way to do this?