Today you can toggle Headings as an allowed block in a Structured Text field. That allows all level of heading or removes all of them. We would find it super useful if you could toggle specific heading levels. This is so content creators cant add a heading level that we don’t support, or add more than one H1 by mistake etc.
I know that we could probably write a plugin to validate this but would still be a great level of customisation to have 
hey @felicia.moller have you considered customizing the structured text fields with a plugin to have your custom styles: Plugin SDK - Structured Text customizations - DatoCMS Docs ?
You could remove the standard headings and add your custom ones via the plugin?
That sounds like a good option, will look into that 
Thank you!
same request also here: Request: Select individual headings for Structured Text editor - #3 by mat_jack1
and here: Limit amount of headlines in structured text fields
