Webservice and core function parameters

I am running moodle 3.4 on centos, and will be implementing webservices using Rest API for our server.

I have listed out the core functions that we will be using, however we seem to need some additional fields such as Cohort Start/End Date or Employer ID/Employer name.

In the DB I can add these columns to store these data but I am wondering how can I tweak the REST parameters to POST/GET these parameters?