The Piano Technicians Guild Journal this month has a note in the Tips,
Tools & Techniques section from Kevin Fortenberry, RPT, of the Heart of
Texas Chapter about pulling new strings through a clean rag treated
with FLITZ polish, followed by pulling them through a dry rag to dry
them before installation, to protect them from rusting.

Additionally, rubbing strings that have light rust in a piano with FLITZ
may remove and protect them also.  I would suggest at least trying
this, and of course do your best to remove the excess polish with a
clean cloth.

Allen Ford