upgrade and downgrand auto billing?

upgrade and downgrand auto billing?

If I were to subscribe to authorize.net and use the auto billing,
would I be able to upgrade/downgrade my clients billing?

For example:

My clients have the option to add on services (which bill monthly).

A monthly plan for example is $50/month
but the client wants to add on an enhancement that is an additional $10 per month = $60/month.

Would I be able to append onto an existing subscription (auto bill) - or would my client get multiple billings?
I have several add on options and I am trying to just have 1 monthly payment not 10 different ones for the same client.