To preface this, I haven't read the lua...
Surely the addon has to save something, somewhere? It seems likely that it saves the encrypted string you paste in to some text file, and decrypts each time you log in. Otherwise, you'd have to paste in your string and import the guide manually every single time you log in.
So surely someone who bought the guide & imported will have some form of file store? If so, you could simply run the decryption methods externally (copy paste job) and save the output to a text file, then remove the DRM from the addon and load this outputted file as normal?
I'll be taking a look at the .lua tomorrow, just thought I'd leave this here in case someone knows already.