Decompiling and modifying a binary can be illegal itself under the DMCA in certain circumstances.

...and so is going over the speed limit.

Practically? Who gives a flying fuck.

PC magazines in the late 80s and early 90s told people how to patch binaries to fix bugs or enhance functionality, with lists of offsets and bytes. Without distributing the original, so no copyright issues there. I don't think anyone tried to go after them because they'd be fighting the 1st Amendment.