Hi there,
It seems that we cant change Announcement on the backend currently as those editor's for each apps will always use "TinyMce" editor and if "TinyMCE" disable, it will use "Editor - None" instead. But it would be best if you can submit a feature request regarding this issues in our voice page ->
http://stackideas.com/voices, so everyone else could vote for it, the more people request on this, and we will priority consider it. Thanks for your understanding