I dont change the length, but I ride quite short at home dressage wise because thats the length I have to have them out because of my boots! Id like to drop them a hole but I cant compete in my boots at that length so have to put up with riding a bit short at home!
But my boots are so stiff, they are lovely but taking ages to wear in (ive had them at least 2yrs!) hence me wearing my old soft ones for XC and for hunting tom!
Because I have a thinner sole on the show boots than on the home boots (which are full length too incidentally, you know those lovely arait glacier style)
I have been putting them up one hole but think its the same reason as Holly_Jane my boots are new and I feel like I have to streatch (sp) more to reach the stirrups. In my jod boots and chaps I dont have too at all. Think lots of riding at home in them to try and soften them around my ankles