What happens if you have a workflow in progress that you want to change the implementation of? Eg. If I had a workflow that was waiting for 30 days but then decided I wanted that interval to be 7 days instead?
Temporal determines a workflow is non-deterministic if upon code replay the high-level commands don't match up with what happened during the original code execution. In this case, technically it's safe to change the code this way because both still result timer commands. But what the timer was first created with on existing runs is what applies (there are reset approaches though as mentioned in other comment). However if, say, you changed the implementation do start a child workflow or activity before the timer, the commands would mismatch and you'd get a non-determinism error upon replay.
After you deploy the new workflow code, you can reset [1] a workflow's execution state to before the DelayAsync statement was called, and then the workflow will sleep for 7 days from now.
That doesn’t take into account the time it’s already been waiting. For when you want to do something on a schedule and be able to edit the schedule in future, there’s a Schedules feature that allows you to periodically start a workflow, like a cron but more flexible. [2] In this case, the workflow code would be simpler, like just ChargeCustomer() and SendEmailNotification().
