I feel like Bethesda games make it difficult to be bad. In order to progress through the game a lot of the time you’re pushed to be the good guy at least briefly.

That’s true, it would feel as if the character had a split personality.

There’s this guide on nexus. Haven’t tested it myself, but I think it’s worth taking a look.

I think that a mod that lets you ask for something (money, knowledge, power…) when a NPC asks you something would be a good start. It won’t make you evil, but it would help to make you feel less good.

For example, a mod that lets you demand Jarl Balgruuf to make you Thane when he asks you to kill the dragon before killing the dragon. The outcome would be the same, you would be Thane either way, but this would feel like you’re acting seeking your own interests instead of helping because you’re a good guy.

Mods that let you lie, like Silence is Golden, would also help.