I ride in my Sportive II boots at unaffiliated level competitions and believe they are approved for all competitions. Don't think you can in High Riders, though not sure!
I have ridden in bothHigh Riders and Sportives for British eventing and BSJA - and in my Sportive's for BD. never had any problems. Only got a comment unaffiliated show jumping - but it was only the owner of the competition venue being a complete pain - if you check the rule book it only states long brown or black boots, and how they mush fit your stirrups - nothing against High Riders