Enrique (poirot), who - for newcomers who might not know - among other things, is the owner of princed.org, has recently created a document that describes how to use CusAsm.
Download links: PDF (mirror), ODT (mirror).
I'll also add links to these on CusAsm's webpage and on popot.org's page about CusAsm/CusPop. [Edit: Done.]
How to crack pop1 with CusAsm
Re: How to crack pop1 with CusAsm
Since the tutorial given deals with moving the shadow in level 6 to another screen, the title doesn't seem all that accurate. I suggest titling it "How to modify PoP1 with CusAsm" instead.