Think twice
Imagine what is happening to your body when you fly with a cold
Before takeoff, the pressure outside, and inside your head/ears is equal.
After takeoff, the pressure outside reduces; under normal circumstances, (without a cold), the eustacian tube allows the pressure inside your head to equalise with the now reduced pressure outside. If the eustacian tube is blocked, it cannot do this, so there is a pressure differential. After takeoff, on ascent, this will mean that the pressure inside your head is greater than the pressure outside, so your eardrum will push outwards.
The greatest problems arise on descent, however; the pressure in your head, (if not equalised by the eustacian tube), will now be less than the pressure outside, causing the eardrum to push inwards, and possibly rupture.
Don't do it - it is simply not worth the risk