Thank you!
Module “Apply Owner Scale to Attributes” works great for me.
I first tried with the script “EasyScale_MS” described earlier in the thread and it was working for the most part. However, I was scaling the owner of the niagara system over time, and I had some particles that were only spawned as instantaneous spawns, not over time. These instantaneously spawned particles never scaled in size over time as the owner was scaled.
I think the script “EasyScale_MS” could be adjusted to work with my scenario, but since module “Apply Owner Scale to Attributes” worked so well I will stick with it.