Where refitting is done depends on many factors, one of which is shipyard availability. However, Navantia shipyard in Cadiz has done a couple of the upgrades and has more upcoming because it is more efficient and cost-effective. They are building expertise with these specific modifications within the work force, as well as built-in construction and engineering efficiencies.
I don't know if Brilliance will use Navantia. I read it depends on how much work needs to be done. Some ships will need less work than others, and so might be done at other yards.