How to customize tinyMCE buttons on Rich Text tilesΒΆ
You can change the buttons that are shown on Rich Text tiles.

Just add something like that to your registry.xml:
<record name="plone.app.mosaic.app_tiles.plone_app_standardtiles_html.available_actions">
<field type="plone.registry.field.List">
<title>Available actions for my html tile</title>
<value_type type="plone.registry.field.TextLine" />
</field>
<value>
<element>toolbar-bold</element>
<element>toolbar-italic</element>
<element>toolbar-bullist</element>
<element>toolbar-numlist</element>
</value>
</record>
When you reinstall plone.app.mosaic the default buttons are shown again, so you have to reinstall your product too.
You can find more names of tinyMCE buttons in plone.app.mosaics registry.xml.