Could you share a bit more context about the mess? Which information exactly do you want to clean up, what's missing, what's wrong? The more details, the better community members like myself can help.
Generally, exporting, cleaning up and re-importing works fine. During the clean-up period, however, records might be worked on and further updated in HubSpot directly by other users. That would be a potential risk.
As another general tip, when exporting, cleaning up, re-importing, make sure to keep the Record ID. When re-importing, you should map the Record ID so that HubSpot updates the records in their existing place. The record ID is a unique identifier, along with the company domain name but more reliable – especially if you are potentially also cleaning up company domain names or companies are missing the domain.
Best regards!
Karsten Köhler HubSpot Freelancer | RevOps & CRM Consultant | Community Hall of Famer