Usually for stock semi-autos that shooters have done modifications to not allowed for SSP but are still allowed within IDPA rules.
Been a lot of discussion why Glocks & M&P's etc fit in SSP but an XD doesn't. This is what Ken Hackathorn wrote on it:
For Stock Service Pistol Division, DA pistols are required. The Springfield Armory XD is a design in which the trigger only releases the striker; it does not cock or retract it...Thus the XD is a Single Action...Glocks are DA because, while the striker is partially pre-cocked, the trigger does retract the striker a short distance before releasing it. So we consider the Glock DA and it is placed in Stock Service Pistol Division. I have had people argue that the XD’s trigger not only releases the striker but also moves the firing pin safely out of the way. Thus, they argue, the XD should be considered a Double Action pistol...
http://www.idpa.com/tj.asp?ID=110ESP
Handguns permitted for use in this division must:
A. Be semi-automatic.
B. Be 9mm (9x19) or larger caliber.
C. Have a maximum unloaded weight of 43 oz., including an
empty magazine.
D. Fit in the IDPA gun test box measuring 8 ¾” x 6” x 1 5/8.”
with an empty magazine inserted.
E. Be loaded to the division capacity of ten (10) rounds in the
magazine plus one (1) round in the chamber. Should division
capacity not be achievable because of lower magazine
capacity, load should be to maximum mechanical capacity of
magazine plus one (1) round in the chamber. Competitors
must use the same capacity magazines through out the
competition (Example: if you start with a 9 round magazine,
you must use that capacity magazine throughout the match).
Pistols approved for SSP may also be used in ESP and CDP
depending upon caliber, even if the pistol in question has a fulllength
dust cover. However, should the pistol in question have a
modification that removes it from SSP, it must meet all other
division criteria for ESP or CDP, again depending upon caliber.
PERMITTED Modifications (Inclusive list):
1. Sights to another notch and post type (see “sights” in
glossary for further information).
2. Grips (no weighted grips; see “weighted grips” in glossary
for further details).
3. Internal accuracy work (includes: replacement of the barrel
with one of factory configuration, the use of Accu-Rails, the
use of Briley Bushings).
4. Internal reliability work.
5. Checker frontstrap and backstrap.
6. Checker or square and checker trigger guard.
7. Cosmetic checkering/serrating.
8. Extended thumb (may be ambidextrous) and Beavertail grip
safeties.
9. Extended magazine release (button may not be oversize in
diameter or protrude more than .2” out from the frame).
10. Factory installed cone style barrels on pistols with a barrel
length of 4.2” or less.
11. Full length guide rod manufactured of material that is no
heavier than common steel.
12. Hammer and other trigger action parts to enhance trigger
pull (includes the use of over travel stop).
13. Beveled magazine well and add-on well extensions.
14. Custom finishes.
EXCLUDED Modifications (NON-Inclusive list):
1. Full length dust covers of carbon or stainless steel.
2. Oversize diameter magazine release buttons.
3. Trigger shoes.
4. Slide lightening (see “slide, lightening” in glossary for
further information).
5. Refer to Appendix ONE-A. Firearms-Non-IDPA-Legal
Modifications.
http://www.idpa.com/Documents/IDPARuleBook2005.pdf