Series: Edit series details after it’s been created
What it says. You should be able to edit settings for your series after it's been created. This would include changing the scoring system and any other settings.
This feature is included (or this issue is resolved) in the upcoming version of Match Play. That version is not yet available to the general public, but it’s possible to sign up as a tester by filling out this form: https://forms.gle/w1FGvQ2sM5YtAzrf6