I can only see the possiblity of a tax liability if you're changing your address because you've sold your home and moved, and you haven't lived in the old home for long enough to claim roll over relief on the purchase of your new home i.e. 3 years. Eithey way, if you sell your main home and
1. you've owned it for more than 3 years
2. you've been resident in Spain for at least 3 years (read as 3 resident's tax returns filed) and
3. you're over 65
....then there's no CGT on the gain made when you sell your home, even if you don't buy another property.
If you're changing your address for any other reason e.g. you are moving between rented properties, then there won't be a tax liability.
Trust this helps