JS injection for field replacement

Hello CCO experts,

We are trying to replace search fields in the Advanced Search with dropdown boxes via CCO Plugin. And it comes to a problems with Javascript - our injections doesn't give us any changes in objects.

I would like to ask, if you have faced similar cases and if you can provide working JS code (just a main statements). Or may be some suggestion, about coding approach.

Unfortunately, it comes to a troubles for a developers.

Thanks in advance!