Hi,

It is surely possible in lucid dreams
Probably most of psychological problems yet surely not disorders can be solved through lucid dreaming
By disorders i mean stuff like schizofrenia or ocd i guess...

There are three stuff that you need for that:
1. Lucid Dreaming (Being Able To Lucid Dream)
2. Dream Stabilization (Be Able To Stabilize Dream So It Won't End Instantly Or In Mere Minutes?)
3. Dream Control (Be Able To Do Stuff Like Spawning Dream Characters etc.)

For 1st a technique of choice
For 2nd a dream stabilization technique of your choice. I personally would suggest you this one:
Dream Stabilization and Clarity Tutorial - Lucid Dreaming - Dream Views
And for the third one just know how to affect dreams the way you want to. I personally would suggest you this guide if you want some good results:
http://www.dreamviews.com/dream-cont...-tutorial.html

- Goodluck