Hello from HubSpot! As of today we’ve enabled Line Item custom properties for all portals, including calculated property support for those tiers that include them. This allows better modeling of Line Item-only properties (such as around discounting), defining calculated properties to minimize manual work or conditional properties to collect required information. To get started, go to Settings > Data Management > Properties and Select Line Item properties from the dropdown. Read more here: HubSpot Login and Sign in
This better unifies Line Items with other CRM object capabilities. There are related asks on supporting field-level permissions that is being planned, and the supporting a custom formula to set the unit price/discount/amount that is being explored.