What about rule 21.2b
Remains in effect – a slide may be modified specifically for the purpose of installing sights, and for no other purpose.
That is USPSA rules.
IPSC does not have that many rules for Production. There is:
16. Original parts and components offered by the OFM as standard equipment, or as an option, for a specific model handgun on the IPSC approved handgun list are permitted, subject to the following:
16.1 Modifications to them, other than minor detailing (the removal of burrs and/or adjustments unavoidably required in order to fit replacement OFM parts or components), are prohibited......
http://www.ipsc.org/pdf/RulesHandgun.pdf