Is there any way to update process Calendar using process Model without giving the administration access to user by using interface.
Discussion posts and replies are publicly visible
It looks like it may be possible using community.appian.com/.../calendar-io
Otherwise, you could try writing a plugin.
docs.appian.com/.../CalendarService.html
Not out of the box. As mentioned by another user you can write your own plugin or see what is out in the market :-)