Can you clarify what you mean by "lug-nut extenders"?
If you mean true extensions, where each lug-nut screws on and has its own threads for regular lug-nuts, those are no good. I wouldn't even drive on the freeway with those.
If you actually have wheel adapters, which are bolt-on rings with their own studs, those are generally safe, however they can cause early failure on a semi-float axle since they still increase the load on the bearings.
2000 Ford E450 V10 VAN! 450,000+ miles
2014 ORV really big trailer
2015 Ford Focus ST