My practice is to always loosen the strings of any stringed instrument I send at least by "five notes". Retuning at the delivery end is no big thing, but damage due to temperature changes and such can really ruin "new instrument day."
Yep, loosen them. You never know if that parcel is going to sit in a stinking hot truck for a day, or in a freezing cold and dry cargo hold at 35,000 feet.