If you shoot in IPSC Production division, the rules are as follow (as it pertains to base pads and other add-ons):
16.2 Magazines accessible to a competitor during a COF must not contain more than 15 rounds at the Start
Signal. Identifying marks or decals, internal capacity limiters, bumper pads and additional witness holes,
which add or remove negligible weight to/from magazines, are permitted.
and
17. Aftermarket parts, components and accessories are prohibited, except as follows:
17.1 Aftermarket magazines are permitted, subject to 16.2 above.
17.2 Aftermarket open sights (see Rule 5.1.3.1) are permitted, provided their installation and/or adjustment
requires no alteration to the handgun.
17.3 Aftermarket grip panels which match the profile and contours of the OFM standard or optional grip
panels for the approved handgun and/or the application of tape on grips (see Appendix E3) are permitted.
However, rubber sleeves are prohibited.
17.1 Aftermarket magazines are permitted, subject to 16.2 above.
Rule 16.2 should permit you to use any base pads for your Glock magazines ie. Magpul, Taran Tactical, provided they don't increase capacity.