Sure, there are plenty of rules for safety on the cars. I'm just talking about general design (that still falls within the safety parameters). For example, you can choose to run a front-engine dragster in TAD. The rulebook even has provisions for it. However, nobody who values being competitive is going to choose that route. You can also run a 150" wheelbase shorty. Again, it will never be done unless someone wants to be a novelty.
Looking at the rules, it seems that TF is more restrictive than I realized. Especially since it says right in the beginning of the section that it is the intent of NHRA that no future performance-enhancing design changes will be implemented.