No, a steel guide rod is not allowed in SSP. The only changes you can make to a gun is SSP are the ones listed in the rule book.
PERMITTED Modifications (Inclusive list):
1. Sights may be changed to another conventional notch and
post type (see “sights” in glossary for further information).
2. Grips may be changed to another style or material that is
similar to factory configuration (no weighted grips; see
“weighted grips” in glossary for further details).
3. A slip-on grip sock and/or skateboard tape may be used.
4. Internal action work may be used to enhance trigger pull as
long as safety is maintained (no visible external modifications
allowed).
5. Reliability work may be done to enhance feeding and
ejection.
6. Internal accuracy may be worked to include replacement of
barrel with one of factory configuration and original caliber.
7. Plastic plugs may be used to fill the opening behind the
magazine well.
8. Custom finishes may be applied.
NOTE: The slide releases and magazine releases that are standard
on the Glock 34 and 35 models are available as a factory option on
all Glocks available in the USA.  Because of this, that type of slide
release and magazine release are legal on all Glocks for SSP

Jed