If the necessary co-ordination has been carried out with the relevant agency, particularly if the flight is in regulated airspace, it poses no problem. In certain UK sectors it is not at all unusual to utilise "opposite direction" levels [or ODLs] as a matter of routine. It enables a large amount of traffic to cruise at or fairly close to optimum economy level. During the early part of the morning, for example, most jet levels are used for the eastbound Atlantic rush......about mid-morning there is a switch to using most jet levels [irrespective of directional convention] for the westbound Atlantic rush.
In your specific case a controller will always make the extra effort if you have an icing problem. In other parts of UK airspace the airway base may be so high as to preclude choice of "unpressurised" levels....the use of ODLs allows best and efficient use of airspace to the benefit of all users.