If you took the obfuscated code, did your best to unobfuscate it by applying both automatic reformating and manual editing, and then made some functional changes in it, or even non-functional changes, such as adding comments, I think you could then claim that what you have created is now the "preferred form for making modifications" to the new, derived work. Problem solved.
You could compare this with the case where a program was originally written in Pascal, but someone automatically converts it into C and starts making changes in the C version. Then at the least for some people, the "preferred form for making modifications" would be the C version and not the Pascal original. Edmund
