If it works for you - fine. I don't think pre-grieving is something that will prevent me from grieving my remaining parent when the time comes. Or beloved bff. I don't believe one can practice it.
I don't think it is even a good idea. I do not go to therapy to prevent me from it. Fortunately the two I see do not seem to believe it is possible either - they have both said they do not. And even if I thought the first was just being wily, the second usually is not.