Does freezing butter or margarine change the properties?
Butter and margarine freeze perfectly.  I generally stock up during sales and thaw it as needed. You just have to make sure it's wrapped tightly in the foil, to prevent oxidation.  It'll keep at least 6 months, probably more if you don't have a self-defrosting freezer.

Thawing butter does take quite a while, however.  I usually give a package a few days to thaw fully. If you need butter in a hurry, you can always put it in a Ziploc bag and fast thaw it a bowl under running running water.  Or, just soften it in the microwave.