[GNC] Convert credit cards as expenses to credit cards as liabilities?

[ornd25 at tutanota.com]

Can I convert credit cards as expenses to credit cards as liabilities reasonably easily, or is my best choice to start doing it properly now and leave the old transactions alone?

I have just started with GnuCash and have imported and hand-massaged 10 years worth of records from two other financial managers. In them I was tracking only Income and Expenses and therefore treated credit cards as expenses in a simplified manner, that is, one credit card entry per month per credit card in Expenses:Credit Card and one entry per month paying that bill from Bank:Checking. Each Bank:checking was reconciled, and Expenses:credit card was not reconciled. 

There are two credit cards so Expenses:credit card has approximately 240 entries for 10 years.

I intend to continue with the simplified approach per the documentation, so I won't be entering individual credit card charges, just the monthly amount.

MY first thought was to change Expenses:Credit Card to Liabilities:Credit Card, but then I'd be left without an Expense:Credit Card.

I actually don't mind manipulating 240 transactions, but entering 240 of them invites errors.

Do I have a way to do this? If so, please explain simply, remembering my newbie status.

Thanks.