Valve has never discouraged the TF2 community from being creative and modifying the game. Team Fortress was originally a mod based on id Software’s Quake Engine. Valve also has allowed for community-made items. As such, you can modify your HUD without facing any consequences. The community has unleashed its creativity by modifying the game in various ways. ToonHUD and HUDS.TF are only two of the most popular methods. There are still many themes and scripts out there for you to use.