Once you have the appropriate disguise and charisma, you should be able to access lower descriptors of your appearance using the appear command. i.e. appear ugly/plain/good-looking/etc.
|a||Mench||8m||Doing a bit of everything.|
|-||ReeferMadness||5h||May the bridges I burn light the way.|
|And 29 more hiding and/or disguised|
I think this is acceptable, but if you can pretend to be ugly you should also (with enough skill) be able to beautify yourself to pretend to be more attractive (real life make-up already works like this).
Also I don't think this would work along with disguise items that hide your facial features for obvious reasons.