Hello, I would really like to be able to change the [Broadcast] prefix, but can't seem to find a setting for it anywhere.
Thank you!

Copy messages.properties (or the relevant messages_zz.properties file for other languages) from the EssentialsX repo to the plugins/Essentials folder, and edit the strings as desired.

You can change it with all other messages if you use the "messages.properties" file.

Oh! Thank you! Is there a way to change how the social spy messages show? I'd like them to be greyed out but I can only find an option to change the socialspy prefix

The "new" social spy system still doesn't allow this even though PR #1226 was proposed a while ago to allow this.