I just realized that the version of Replaymod I've been using (2.0) is several iterations old, though as far as I'm aware the existence of an update was not announced anywhere. Is there a way to let users know when there's an update? Additionally, I have no clue what's different between 2.0 and 2.1.4, are there changelogs somewhere for new updates?
Forge should automatically query this file when you start Minecraft and display a small blinking emerald on the "Mods" button in the main menu if your version is older than the latest recommended version:
Same should go for pre-releases if you currently have a pre-release version installed. If the latest version is a release version and you'd like to be notified of pre-releases, there's currently no mechanism for that afaik.
There's no mechanism for snapshots other than regularily checking the thread in which I've recently posted a snapshot link (I usually post snapshot links only in specific threads for specific purposes, e.g. specific, low-priority bug fixes or the 1.14 version).
The thread which contains a summary of all changes for each update should be linked on the Download page (close to the bottom).