[CT]

If it's a single-piece wheel, you're probably OK. Most manufacturers use the same forging or casting blocks for each "set" of diameter/offset/width combinations. For 18x8.5, as an example, you might have the same forging die or casting mold for 20mm to 30mm offsets. The post-forming operations would mill down the 20mm offset to 30mm prior to finishing. Removing an additional two or three shouldn't be any issue. Standardizing tooling is an extremely common cost saving move.

If it's a two- or three-piece wheel, you're likely to have greater risk because the smaller forging dies are much cheaper and it's easier for the manufacturer to employ greater variety. The greater variety allows them to employ more aggressive design allowables.

TL;DR - It's probably OK, to the tune of 2-3mm. Damage will be from fatigue life or extremely high impact load (avoid bumps, lad). Any more than a tenth-inch or so and you run a much greater risk.