Can I refreeze gravlax made from previously frozen salmon?
Yes, it's even recommended to use salmon that has been frozen for at least 24 hours to make gravadlax as a precaution against parasites, since the salmon isn't cooked. (Of course I'm assuming that you want some right away!)
Prepared gravadlax freezes very well. As Jenna says, wrap it individually in cling wrap, and freeze for up to a couple of months for best quality. Refrigerate it for a few hours to thaw before serving.