Performing mass updates of Item/Vendor/Customer Cards

Is there a method to perform updates to thousands of Customer/Vendor/Item cards all on a large scale? I know rapid start allows for importing new records, but I can’t find any documentation that indicates it can be used to change only a few fields of cards that already exist, like would it have problems validating in import?

I want to to be able change things like the Production BOM No., Production Routing No., lead time, reorder point, max inventory, reorder qty, weights, scrap %, etc, on the item cards, and fields such as Credit Limit, Payment Terms Code, Collection Method, Payment Method, in Customer Table. If I can’t use RapidStart, is there another tool I can use to update these fields in a mass/batch mode?

Thanks for any help that can be rendered!