It's possible to execute an I.r refer on a non-production environment then replace the production IR index. After taking the database copy you need to suspend I.r indexing on Prod, then complete the new indexes m, migrate them to prod, and the re-enable indexing to index the records from the interim period. I think there are instructions in the SM Help Sever.
note that you may also want to remove the journal led history fields from the IR Key (e.g. Update.action in probsummary). A as it can significantly improve performance.
if you have Knowledge Management, you have the option to index tickets using the KM index, which removes the need to use IR indexing (and provides a much more sophisticated search capability).