I believe that this question falls under the answer “Don't do it man!” because you are likely to hurt yourself. The reason that these are locked down is because there is hard coded logic that uses the codes. For example, the Customer Type field has three options, and the software AUTOMATICALLY changes the customer from “Suspect” to “Prospect” to “Customer”. When you first create an entry, it defaults to Suspect (you can override)… when you create a quote, it automatically changes to Prospect. When you convert the quote, or enter an order, it will automatically convert to a customer type. Anything outside of those three options are likely to break something. Same goes for other fields such as the Make/Purchase codes in Parts, and other fix set values. They are fixed for a reason.
If the data if flexible, then there is a setup table to maintain that data.
So… Don’t Do it!