Changesets cannot be "duplicated" because UUIDs are, of course, unique

[postphotos]

If using a plugin like "Duplicate Posts" and you clone a Changeset and then try to edit it, it throws an error: Invalid changeset UUID.

1. This is perfectly valid behavior and it makes sense why, but can we, in the meantime, provide a warning in the release notes?
2. Further, can we add functionality to prevent plugins like "Duplicate Posts" from using this post type in the method followed in time for the 4.9 WP Core release?
3. Finally, can we add a working duplicate feature? Use Case: Imagine having Changeset-1 getting cloned and pruned into Changeset-1a and Changeset-1b.
4. Similar functionality to merge Changeset-2 + Changeset-3 into Changeset[2 +3] would be great as well.

[westonruter]

Actually, providing a way to copy a changeset has already been suggested in #41 with implementation in pending PR #90.

[postphotos]

Yes! Thanks @PatelUtkarsh @westonruter for your awesome contributions! - this is also related to #118 and #93 as well. Essentially, we're after a similar branching pattern like we see in git or other structured version control systems. Split, merge, fork, branch - as much as we can, mirror workflows that folks are actually using in publishing and dev spaces.