Sure, why not? As long as it’s valid you can use it over and over again.
You can download avast! separatelly anyway, you have to enter key later.
So no problems.
The registration doesn’t take long and would give you a full 14 months of VPS Updates, avast! 4 Home Registration form and you will receive an email from register @ avast.com (without the spaces) with your registration key.
Everything is back to normal. Downloaded the avast (home edition ) program and copy/paste my old registration key from the first e-mail of register@avast.com.