Mostly not covered by this source. Rims with an adapter need validation, and a centre-lock conversion kit and wheel spacers are not allowed.
Inspection neededYes
Certified part neededNo
What you need to know
Rims with adapter: fixed adapter on the rim, suitable vehicle, solid mounting, validation procedure.
Widebody kits: keep the legal distance of lights.
Fenders: enough wheel cover.
Normal rim size rules are not covered here.
Mounting a wheel with a centre-lock kit, or a rim with an adapter that is separate from the rim, is on the Flemish list of things that are not allowed.
Widening the track with wheel spacers is also on the Flemish list of things that are not allowed.