You need to be REALLY careful changing data structures because it potentially makes you an "orphan" in terms of any future updates. If possible, the first choice would be to take advantage of existing unused fields and files. Second, add additional files to the database that have the structure you need and can be linked to existing files, and finally as a last resort, change the structure of existing files.
There is a TAS6 program that runs the first time you load Evo that reads the DBA data dictionary and constructs the codebase dictionary but my understanding is, it already has the structure of the files and fields defined and is only reading FILELOC.B to establish the paths to the different companies. There is a "clean" set of DBF/MDX files available at
http://www.istechsupport.com/datadict.asp