I run 88mm Omegas.
If you're on about declaring an engine mod then IMO it's how you feel. In my mind it's just a biggish over bore so it's still a 2ltr wih bigger pistons, so I wouldn't really worry about it (although I do declare it cos my insurance would pay for a whole new engine).
I would declare an engine increase if I I changed something like a 2 ltr block to a 2.5 or something.
Technically the 88's are talked about as taking it to a 2.1 though but IMO people say it for the tech spec rather than any technical reason.