Can I mix monthly and annual terms for different products under one CSP account?

Yes — billing terms are set per subscription, not account-wide. You can have, for example, Microsoft 365 licenses on an annual term while keeping a smaller set of seats on a monthly term for contractors or seasonal staff, all under the same CSP partner and consolidated invoice.

This is actually a common way organizations balance cost savings (via annual terms for stable headcount) against flexibility (via monthly terms for variable headcount).