Yes, I have basically increased the size of the opening as alternative to drilling holes on the side of the box. I wanted to allow more air in and at the same tome to have an opening on the top of the box.
I test rode the bike immediately after I assembled it back and I think there is improvement in the feeling for power (could be just physiological) and more throaty sound. And all this with OE cans.
Hope this helps.

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that is how i feel about my XTR
Mods so far:
Hyperpro front springs; Hyperpro rear shock spring; modified air box; LED tail light; LED indicators + new relay; YZ pegs; Lucas aluminum bar; brisk spark plug; snorkel removed; DNA stage 1; second hand DynoJet O2 mod; crash bars; front and rear steel braided brake lines; soft EBC brake pads; mitas 07 tyres, 2in1 Metal Mule exhaust, Blocked AIS, tall OEM screen, OTR bash plate