I bought an expensive algorithm that automatically buys and stocks for 10,000. It runs on my PC. The seller is a goy. The files are encrypted. What I want to know is if is can unencrypt it and then improve upon it. They already got paid and I’m not reselling this to others so it’s not detracting from their income, I just want to hire my own improvements to improve upon some things which I know I can do giving me a better roi.
Yes, this is fine.
The algorithm is yours and you are within your rights to do as you wish with it. This is similar to somebody who sells you a book; of course you can change the text at will. The same is true of a digital creation.
This answer does not depend on the Jewishness or otherwise of the seller.
As noted in the question, the answer refers specifically to personal use and not to selling on to others.