Modifying the Character Collision Bounds In the screenshot above, I have Suzanne as a character with cylindrical collision bounds. However, this is too large for me, and I want to make it narrower (along the X and Y axis) so she can go through doors and such. 

I'm aware that I can parent the green cube to her and have that as the collision bounds (with the box itself having cylindrical bounds of course), but this will cause it to glitch out and flying away due to Suzanne and the box colliding with each other (Suzanne has a character physics type, and the box has a dynamic physics type). I am aware of the workaround by assigning all the game logic to the cube, and parent Suzanne (as a dynamic physics with "ghost" activated) to the cube.

My question however:
Is it possible to edit the size of the cylindrical collision bounds of Suzanne directly? Without parenting Suzanne to another object that will behave as the collision bounds? (The collision bounds of Suzanne is the octagon in wireframe around her).

Those who are familiar with engines such as UE4 and Unity know what I'm talking about here.
The sizes of the bounding box types directly rely on the shape of the mesh. In your case the cylinder will align around suzanne's mesh. 

Be aware Cylinder will be symmetrical on single axis. This means the origin of the object should be in the center of the mesh. 

The Cylinder type is homogeneous on X and Y axis too. This means the shape will be a circle rather than an oval. 

Therefore the Cylinder fits most to meshes that forms a nearly a cylindrical shape.

The alternative would be convex hull or triangle mesh (needs more calculation power).

Another alternative is to assign a custom physics mesh (e.g. via parent actuator).