>It seems pretty straightforward to write a method to evaluate any REG_EXPAND_SZ value type since the variables are surrounded by %variable_name%.
>

AFAIK, there's nothing in the FFC registry class or REGISTRY.PRG to handle anything except REG_SZ key values. I've written more generalized routines before to handle various data types - it basically involves retrieving the value type in the API call as well as a buffer large enough to handle any possible binary return (REG_MULTI_SZ and REG_DWORD, for example, may contain embedded nulls that would falsely terminate a C-String.)

>Does an updated version of registry.prg already exist that returns REG_SZ and REG_EXPAND_SZ value types? If not does a complete list of registry variables exist? How do I retrieve the values for these variables?

The complete list of REG_EXPAND_SZ values is impossible to create, since -any- environment variable can (and often is) used in REG_EXPAND_SZ key values.