All fields in managed objects are system fields, except for explicit override mechanisms that CPQ provides through user input or APIs.
The following are some examples of the fields for which CPQ accepts user input through the out-of-the-box CPQ UI or globally exposed APIs:
Price List
Quantity
Term
Start Date and End Date
Coupon Codes
Adjustments
Base Price Override
Product Attributes
Except those fields that are available to be modified using the out-of-the-box CPQ UI and APIs, all other managed fields are system fields. Therefore, you must not manipulate them because of the risk of data integrity issues.
In case you must manipulate a particular system field value because of business requirements, you must contact Conga Support to evaluate if one of the following options is possible:
Is there any existing out-of-the-box mechanism to do that?
If not, explore the possibility of CPQ providing such a mechanism.
If both options above are not possible, Conga Support must get approval from the CPQ Product team so that the Product team can track such fields and maintain backward compatibility when developing an enhancement or fixing any issue related to such system fields.