There is a potential way around this that has often been used by other projects. You make the original game files a requirement for it to work and you don’t distribute any files that include trademarked material directly and instead it uses the original files and modifies/extends them as needed. This has been used for a large number of other projects including things like the Ocarina of Time decompilation project.
It would still qualify as a mod if it required the original game, I’m pretty sure it would be fine to release that way, but it’s probably not worth the risk of legal bullshit.
There is a potential way around this that has often been used by other projects. You make the original game files a requirement for it to work and you don’t distribute any files that include trademarked material directly and instead it uses the original files and modifies/extends them as needed. This has been used for a large number of other projects including things like the Ocarina of Time decompilation project.
It’s a remake that uses new, higher quality assets though, so isn’t an option in this case.
It would still qualify as a mod if it required the original game, I’m pretty sure it would be fine to release that way, but it’s probably not worth the risk of legal bullshit.