You cannot transfer items form one account to another one. All purchase made with that account/Apple ID will always be tied to that account no Apple ID.
The new account will not wipe out all of your current content - you can keep that content - but will get a little hairy if you use the old account in order to download purchases made with account. You may lock yourself out of your new account for 90 days by associating the iPad to your old account.
Read this so you know how a device becomes associated with an Apple ID.