Well, yeah. If it's for private use, nobody is going to know that you did it, right? The whole point is recognition for work that someone did, and avoiding people taking credit for something that they didn't create. If you made a mod to replace Kyle with a model of Obi-Wan only for your own personal playthroughs, it doesn't matter. Any modder out there would probably agree with me that they encourage people to tinker with their mods if it means learning how to mod things and figure out how we did things. (okay, not all would agree to that, but still)