allen ive done the same thing the whole time ive been s/c ed i use a 7 rib and cut 1 off for 6 months now .no issues .but the 1st time i wasnt soo carefull and when i was cutting i slipped a tiny bit onto the 6 rib of it and it did chew it quickly since then no problems,good luck ,and go very slowly when cutting with razor knife ,they slip intoo the other groove ,lay it nice and flat ,if you cut in the least bit of an angle it wont work.good luck hope it helps.
mods:2004 sierra ext sb,20s ,big brake kit w,hawk pads,air bagged,2006 6.0 lq4 swap,vortec supercharged10psi, air to water intercooled w/ dual electric fans on it ,snow meth injection kit,60lbers, e-fans ,big radiator swap ,cam 218 /222 548/550 comp .hardened prs .1.85 comp roller rockers ,guideplates ,crane double springs,trans 4l65e built .pacesetter l/ts true duals w/x pipe and magnaflows,14 bolt rearend swap ,3.73s,aroemotive fuel pump system w/elec.fuel controller and bypass regulator a/n fittings, taylor 10.5s interceptor gauge,aem w/b a/f ,autometer boost/vac NELSON 93 OCTANE TUNED .