So, per-beat effects are on the roadmap. I was hoping to include this as part of the big “Editor 3.0” update that is now in beta testing, but it caused a bunch of problems so I had to postpone that feature until I have time to think through all of the edge cases with enabling per-beat effects.
Normally I recommend not including a pickup measure in the chart, as any notes included should be part of the count-in or the previous repetition of the form, with the first chord coinciding with the first “main” downbeat of the song. It’s interesting to hear that your reason for wanting this is less about what you hear and more about how it looks, for sharing purposes. That is something that I think people are doing more and more (sharing charts/PDFs with Strum Machine) and is something I want to keep in mind for future development.
Anyway, per-beat effects may be coming later this year, but I can’t say for sure yet!