>>881573 (OP)
>Can I look at its source code and mimic the its functionality, writing it so it would "look different" or in a different language without being sued later?
No. This is why clean-room design was invented.
https://en.wikipedia.org/wiki/Clean_room_implementation
>>881585
>I know, but how can one prove that I indeed looked at the source code and not just re-implemented the whole thing from scratch?
They don't have to "prove" it in a mathematical or philosophical sense, or have footage of you looking at the proprietary code. They only have to convince a jury. And unless you can afford a legal team that's at least as good as theirs, they will.