What is the best practice for "projection design modification"

Life is long and there comes a time when you need, for example, to add another projection of events. What is the best to achieve this?

  1. One way is to add another processor and replay events, but one more (same as in other processor) source will be used.
  2. Another way is to stop existed projection, replay all events to existed offset, and start all projections with single source.

I think second one is the best, but I can’t figure out, how it can be implemented using lagom abstractions