Trouble with that is that "at your discretion" only tends to be used when you aren't preapared or qualified to clear someone to do something
eg an AFISO "...land at your discretion"
at EMA we don't clear the Helimed to lift from the pad as its off the manoevering area and we can't therefore KNOW its clear to do so ergo "...lift at your discretion"
Similarly, an aircraft, clear of CAS, not recieving a radar service requests descent .."G-CD nothing known to affect, descend at your discretion"
To use it in an airways environment IMHO would be a little strange and would I think unsettle the crews a little for the reasons given above......discuss