I’ve got the exact same forks as those in the link and you’ll see they’ve got sag markings on the right leg, 80mm, 100mm and on mine you can see that it carries on past the seal to presumably 120mm, so i’d say that its almost 100% likely that yes there is a spacer fitted for 100mm and adding/removing will alter the travel.
HTH but the only way you’ll no for sure is to try, as there may be some OEM ones around that are fixed, however i’d imagine they wouldnt have the different travel sag settings on the stanchion as they wouldnt be needed.