Hi Andrius and welcome to the community!
These fields can not be changed as they have key reasoning behind Pipedrive logic
“mandatory_flag” are fields that an item is required to have or is unable to be created. For instance, a Deal would be required to have an ID field and a Title field.
As of yet, we haven’t implemented creating custom fields that are mandatory.
“edit_flag”: true/false just states whether or not it is a custom field. If it’s true than it’s a Custom field, if it’s false it is a default Field