Hello everyone!

I desperately want to play with mermaids but it annoys me to no end that they swim over the whole town instead of using a boat. No I want to just make them stop and take a boat like every other sim. But unfortunately I dont have any experience with modding and I don't even know where I should start. I looked a few things up but due to my non existing knowledge I dont even know if I looked at the right thing.
What would I need to mod this? Is this even possible? I just need a little headstart so I know what exactly I need to learn to mod this correctly :D

Thanks in advance :D