using CMS.Community;

using CMS.SiteProvider;

using CMS.CMSHelper;

...

        string groupName = "customGroupName";

        string siteName = "CommunitySite";

        // Get group object 

        GroupInfo gi = GroupInfoProvider.GetGroupInfo(groupName, siteName);

        // If group exists

        if (gi != null)

        {

            // Create role object

            RoleInfo ri = new RoleInfo();

            // Set role properties

            ri.RoleName = "CustomGroupRole";

            ri.DisplayName = "Custom group role";

            ri.RoleGroupID = gi.GroupID;

            ri.SiteID = CMSContext.CurrentSiteID;

            // Save role to database

            RoleInfoProvider.SetRoleInfo(ri);

        }

using CMS.SiteProvider;

...

        string roleName = "CustomGroupRole";

        string siteName = "CorporateSite";

        // Get role object

        RoleInfo ri = RoleInfoProvider.GetRoleInfo(roleName, siteName);

        // Get user object

        UserInfo ui = UserInfoProvider.GetUserInfo("CustomGroupMember");

        // If role and user exist

        if ((ri != null) && (ui != null))

        {

            // Add user to role

            UserRoleInfoProvider.AddUserToRole(ui.UserID, ri.RoleID);

        }