I'm not sure. Given all the romhacks of SMW produced in the last couple of years and nobody getting sued (even though the authors are known/popular), I don't think they'd bother with suing for the C64 port. Just search for "romhack" on twitch.tv if you haven't seen those yet.
When it comes to SMW ROM hacks, nobody distributes ROMs. Instead, people release _patches_ which have to be applied to the base ROM (this is done through an IPS/BPS patching program). There's actually a JavaScript version available: https://media.smwcentral.net/Alcaro/bps/
