Is it possible to provide other fields/values other than the fields as specified in the TAPI DocuSign Template Manual?

You can add custom fields in the field 1, field 2, and field 3 parameters for each party, account, and/or trade. These fields can then be populated in your DocuSign Template.

You can add custom fields in the field 1, field 2, and field 3 parameters for each party, account, and/or trade. These fields can then be populated in your DocuSign Template.

TAPI DocuSign Template Manual