Github user afs commented on the issue:
https://github.com/apache/jena/pull/473
@hartig - see PR #507 ; that should allow you to
`ResultSetWriterRegistry.register(SPARQLResultSetText, <YourCodeFactory>)` to
set your own text output engine.
For grabbing the prologue, see:
https://github.com/apache/jena/pull/507/files#diff-6efebeadd02ab276d49ddc9bf99f0758R117---
