How to Copy Multiple Billed Slips from One Client to a New Client as Unbilled Slips

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We have finalized multiple bills (at least 10 going back around a year).  The client has paid our bills but I now find out that the bills need to be submitted in the LEDES98B format to an insurance company so that our client can be reimbursed.

What I want to do is copy all billed slips to a new client and then generate multiple invoices for the insurance company in the LEDES98B format. There are a few hundred slips that once copied will have to be edited to put in the missing ABA codes for billing and also be split in some instances to avoid block billing.  That's going to take a lot of time as it is.

Is there any way short of copying each slip manually and saving the new duplicate unbilled slip to a new client?  It gets very confusing when doing this one slips at a time and it's easy to overlook a slip or make two copies.  I would just like to be able to copy all slips for one client in a certain date range and the only thing that would change on the copied slips is that they would now be under a new client.

I did see a comment somewhere here about exporting slips (in over 25 years this is something I've never done), but it was stressed to make a copy of your database first and be VERY careful about what you were doing.

Thoughts?