Looks like you can do it with the REST API: http://onlinehelp.tableau.com/v10.4/api/rest_api/en-us/help.htm#REST/rest_api_ref.htm#Add_Project_Permissions%3FTocPath%…
Being a cmd prompt programmer that's all I can provide.
Thanks Toby for the quick response
Could you please provide me one example from login to logout. Also, do we need to enable anything to use the REST API functionality ? (ASAIK- Not required) but could you please confirm me
"Being a cmd prompt programmer that's all I can provide." ~Toby, from the above post