Well, it isn't as easy as just turning down the physics, textures, and model sizes and setting the project to the Reach profile.
A good chunk of the QuickStart engine utilizes Vertex and Pixel shaders, and while very cool indeed... unfortunately as still of WP7 7.1 (7.5 Mango) the WP7 does not support unique vertex or pixel shaders...only the built in ones.
So, you would need to also convert all references to the shader code into either one of the existing effects for the Reach profile or in some instances (i.e. terrain with multiple texture levels...very cool guys btw...) you would need to come up with some
other way to handle that...
There are many examples in various forums of different "tricky" ways to implement some of the more common HD (vertex/pixel shader unique) methods, but in the end until Microsoft decides to open up that pipeline it could quickly become a bit of a task.
Although...it would be very cool to see what the QuickStart team could try to come up with regarding a Reach profile version of their engine...
Nicely done guys... very cool example of many commonly used techniques in game development