It'd be awesome if you could archive the current version of a release schedule and then make changes to illustrate the impact of resourcing/ scope decisions and then restore the old version if you don't decide to make those changes. You can currently only save a "dead" copy as a manually updated notebook page. (Unless you can download release schedules somehow like feature lists and I just haven't found it, in which case, sorry).
As noted, one potential workaround would be add a Release roadmap to a notebook, and set the "Refresh" setting as "never." You can create multiple slides with this information over a set period of time to see how the Release schedule changes over time.
With this workaround in mind, we will mark this idea as "already exists."