modify source of copyrighted software

Question

There is a a program that I want to use that is released in two (fully copyrighted) ways:

1. Stable binary form
2. Beta release, mostly-stable binary form that is easy to derive the source (uses jars) (this version is free)

Question:

1. Can I legally download the beta version, make the necessary changes to work properly on my machine, recompile and then use the software?
2. If yes to question 1, can I then explain to people I work with how to do the same thing so that they too can use the product?

In no way would I be giving them the modified software, but rather distributing instructions how to modify it. The original download would still come from the copyright owner.

I believe I have done my due diligence searching these and google's forums, but as always, if you find a duplicate question, please let me know (and point to where it is found). It seems odd to me that this hasn't been covered yet.