I am not a lawyer and this does not count as legal advice.
It is illegal in the united states for anyone not licensed as a lawyer to give legal advice.
Okay now that thats otut of the way, I AM a reasonably knwoledgeable amature havign grown up in an Ip household and havign ahd a long standing inetrest in the area of IP law.
What you are asking about, under US law, falls into the cetagory of derivitive work. If you add new work to an existing work then, what work you add is yours so long as it is significant. What remains of the old work is copyright to the original copyright holder in so long as it is significant.
What is “sgnificant” is up to the courts, so the short answer is that there is no answer prior to a law-suit for a case like yours as to whether a work is considered wholly new or derivative.
Copyrights in a derivative work are seperate to each party such that neither party can legally copy or destribute the derivative work without the others consent.
Note that there is nothing in the law about ‘for profit’. This is a common misunderstanding. Profit may weigh into the damages awared after a Copyright violation has been determiend but play no part in the determination of whether the violation has ocurred.