First, you can go into the Laserfiche Administration Console and uncheck the option to always index newly created documents. Then you can detach/delete the current search catalog and create a new one. Don't index the repository at that point. If you go into your volumes, you can choose to re-index individual volumes if that's how the repository is currently structured to operate, i.e. you only want documents in certain volumes to be indexed.

For future documents, you'll need to configure options client side if you want to index them even if they are already configured to go into specific volumes. There isn't a built in mechanism to only auto index new documents that are created in certain volumes.

With that being said though, can you clarify exactly the types of searches you're running? This is to confirm if the above suggestions are the best course of action. If you can provide some sample advanced search syntax, that would be really helpful.