I might try and pass up the self-harming sadistic ideas, but since you have a want to transform, I would call it needed for transforming. Kind of... let me explain something.
Dream control is often hard to control. You might have a dream that you are controlling fire one night, and not get a spark the next. Some people think that this only happens in non vivid non aware lucids, but after a while, you notice that you can hit a very big wall and not be able to do any dream control in random LDs. If you are aware in a dream, you should be able to control it in what ways that you need. If you go through standard ways of dream control, you might be able to find a way to fly that works for you, and then always be able to do it after practice. This is a problem, because in order to be a master, you don't want to have to do that on every dream control task.
The ideas that dutchy outlines are a way to realize that cutting off your arm is the same as controlling fire is the same as flying is the same as any dream control, because my body is the same as the dream world, and the dream world doesn't really exist unless I say it exists. So instead of learning each and every dream control, we learn one simple way to do each and every thing.
Now omnipotence is boring after a while, but needed if you wish to work in higher levels of dream control. Even if you wish to create a universe with restrictions, you need to have full control at first.
If you wish, I can integrate the pain into your current dream goals.
In this, you could either take your lungs out so that you don't need them in space (actually pretty hard), you could die when you get to space (also kinda hard), or you could skyrocket down to earth and burn up on the way in, maybe make it to earth (quite easy if you are already up there)
Fly into space and look back at the Earth
You could take out an animal heart and put it in your chest (hard), get bit by the animal and let the vampire/werewolf effect take place (pretty easy), jump into a machine (spells and things like that would work as well) that will transform you (expect pain during transformation, difficulty depends on your ).
I can't think of a way to make this painful except for the last way. Or you can always get hurt after transformation.
Transform into an inanimate object
Make sure that the pain isn't just for pain's sake, but for understanding that your body doesn't really exist. When you come to understand that your real body isn't even with you, it will click, and you will know what to aim for in that regards.
I often just tried to get hit by cars and jumped off trains when lucid. Good stuff. Also cliff dove. There is also a chance that you are going to do something like take off your arm with a hacksaw and feel no pain. This will have the same effect, maybe even a better effect.
I would recommend you making sure to pick just one dream control idea tonight. This first part is that your dream body doesn't exist. After this, it would be good to move to dream characters or dreamscape. These are important ideas not to just believe, but to demonstrate to yourself.
On an unrelated note!