You can mix and match roles as much as you'd like, as long as you keep a few basic concepts in mind:
1. Include more Villagers than Werewolves and the Minion combined.
2. Always have a Seer or Fortune Teller, and at least one Werewolf.
3. Don't change roles out between every game. Add or subtract different roles frugally; switching things around too fast can be confusing for players who have to try to remember what roles are in the game.
Here are a few good sample rolesets at different player counts: