Djokovic change his serve at some point in his career, it's not as explosive as it used to be, but it's more consistent and accurate. And that was at the same stage in his career as Iga is right now.I commented on this in the General Messages board before I saw your posts here. Personally I think changing technique at this late stage of the development part of Iga's career is very risky. The technique will be 'baked' into her nervous system. Instead I would concentrate on improving what is there i.e. improve reproducibility and work on variety (as @guitarra suggested), accuracy, and disguise. Much better to build on what is there than go re-tooling, especially since her second serve stats are so good.