^not for a long time. i don't wear them all that much so i don't see them needing any more than a quick hand wash every 8-12 months. that is good to know though. i will probably was in cold water and hang dry given that info.
^ it doesn't sound too hard to do tailor-skill wise. i'll let you know since i'm having my 21cm tailored to a 20cm. i'd be more nervous about it if my tailor didn't have a chainstitching machine, though
it is very easy to add taper to the leg of any jean or to reduce the hem opening. turning a 21cm into a 19cm is a whole other story though. slimming the lower leg only involves opening up and slimming the jeans from the knee down, but changing the entire leg fit is trickier because you need to start all the way up at the thighs.
and regarding sigmatic's chainstitching comment, only the raw diors are chainstitched. the washed jeans are not so any tailor can open the hem on them and put it back together as they were. actually, some seasons of the raw denim are not chainstitched, mainly the older ones.