Requirement columns

I was wondering if you can add more requirement columns to the standard unit table. As it is, you can only truly have 2 requirements for a trained unit and 1 for townhall type buildings. (one is used for the building it is upgraded from and one to say that it is upgraded) Can I add more needed columns and how do I do it.

yes you can. use the neededextra.txt file.

How many additional requirements can I add in the neededextra.txt file

As many as you like. There is no limit.