What happens to data in a field if its rpos changes?

What happens to data in a field if its rpos changes?
Does changing a field's r-code position affect the contents of existing records?
 

It's possible to change r-code position of existing fields via an incremental .df.
Main use case is to ensure all instances of a database (development, staging, various production instances etc.) are in sync.
(The different instances could be pushed out of sync if a .df was loaded which was created without the "Include POSITION ... " option active, or if the schema changes were made manually and fields were added in different orders in different instances.)

From a logical perspective, nothing happens to that data. The same fields will keep the same values.

In terms of record storage: There will be changes in how the record is actually stored on disk and in memory, but those changes are made transparent by the schema versioning/fast schema change features the database engine uses. Those mechanisms will ensure the existing records will be converted from the previous structure with old r-pos to the current structure with new r-pos as needed, so any connected clients only need to deal with the current structure.
 

While the data remains unaffected, changing a field's rcode position will change the table CRC. As a result, code referring to the table will need to be recompiled.

References to Other Documentation:

Progress Article(s):
 Schema Versioning: Why V9 schema changes are so fast
 Cyclic Redundancy Check Explained