I've purchased the 5 motif chalcedony in Paris and brought it in the US boutique to get it shorten. My SA told me I have 12 months to do it and when I received my bracelet back from the adjustment, he told me again that if it feels too tight shoot him a text and he'll help me send it out for another adjustment, free of charge. I guess you should ask the SA be sure.
I can't speak for other countries in Europe, but specifically in Paris, I was told that any purchases valued below €30,000 you'll get 12% VAT, but 16% VAT if you spend over that amount. Considering you'll have to pay back some taxes as you return to your home country, the saving becomes even less significant. Agreed with
@BigAkoya, the small saving in the VAT isn't worth getting it oversea, unless you're going for the exclusive pieces at Vendome or other specific boutiques around the world. I'd rather purchase from a home boutique to build up the profile so I can eventually get approved for SO's and other LE pieces. Last year when they release the holiday pendant, I didn't get offer one in the US because I didn't have a home boutique here, they somehow flagged Vendome as my home boutique because I've made several purchases there throughout the years while on vacation. Vendome did offered me the holiday pendant, but if I didn't already have a trip planned around that time then I wouldn't be able to get it.