Add the plugins to the editor
With your new custom modules active your plugins will be available to TinyMCE to use, now you just need to turn them on.
The location to adjust the way tinymce buttons are displayed is 'form_editor.tpl', there are 2 locations for this, one is in the core and the other is in Site Builder system.
Override these either by skin overrides
Or by using the Template Editor
This method will prevent you from needing to take any action when new module updates come out, your changes will persist.