David,
I talked to the programmer today, and in a TAS 6 environment (which Evolution is) it is possible to have custom functionality that does not actually affect the core code. It is actually compiled into the screen code itself!
AND, the programmer that created TAS language itself, is working on a version of TAS right now that will incorporate what are called Stored SQL Procedures. What that will mean is that anyone could hire an SQL programmer that is familiar with Pervasive and write a custom set of routines and math and even create database fields to store information temporarily and then delete the field all in one seamless operation.
This means that you will be able to (in Evolution, as well as in upcoming versions of TAS 6 programs) be able to do "custom" calculations and a lot more without ACTUALLY customizing the core code.