Yes, you can include the new balance (tax liability) in
your current installment agreement. There will only be one installment
agreement which includes all of the tax
years that you owe.
You should contact the IRS as soon as possible to have it
included because a new balance will automatically default your current
agreement (it is one of the terms and conditions.) You can call them at 1-800-829-7650 or go to a local office.
Or, you can submit another Form
9465, and include all of the tax years that you owe with the request to
have the new tax year included. It is important to have the new tax year
included because collection will start on the new tax year, if it is not added
to the agreement.
See FAQ below for more info: https://ttlc.intuit.com/replies/4678634