This is what we say in the doc http://documentation.magnolia-cms.com/display/DOCS/Rich+text
>> In 5.0. You can use all common field properties but the rich text field is not yet configurable in Magnolia 5.0 so it doesn't have properties of its own. Currently, the editor options are hard-coded, see RichTextFieldBuilder. This field will become configurable in a future release.