Credit Card account merge in Q2008

Yes.

You can select transactions in Quicken non-investment accounts as you would select files in Windows Explorer. You can then use Cut/Paste, Move, or Copy/Paste (in the Quicken "Edit > Transaction" menu) to "move" those transactions to another Quicken non-investment account. [If you have reconciled transactions in the FROM account, I think the Copy/Paste approach will avoid the nag about moving reconciled transactions ... for every reconciled transaction.]

If you wanted to just keep all the data in the old account, you could have (and probably still can) deactivated the old account for download before the first download from the new account. Then the old account would have been available for you to select to put the downloaded transactions in. [You may have needed to clear the account number field in the Account Attributes after deactivating and before doing the download, I'm not sure. If you can do it, you probably should: I don't think it would hurt anything.]

When the dust clears, you can just delete the Quicken account that's no longer needed.

Backup before doing anything.