@texnixe: I’ve got a hard nut to crack for you:
I have a custom block (handled with the block model). I want to to change this view:
(at least the text)
But… 
…in my case i have no change to create a preview template for that.
Why? My blocks gona dynamic create by the dynamic blueprints. The naming of the block can’t be caught by the preview templates.
I hope my explanation makes sense for you.
What do you thing? A thing of impossibility?
Dynamic blueprint or not, your block always has a name and so you can create a preview.
That’s the point. The name isn’t static.
fields:
blocks:
type: blocks
fieldsets:
- this-could-be-anything
The name depends on certain files that the user creates.
I thought maybe there is a property that is a placeholder for the displayed fields.
Same as the columns property in structure
Made a sugesstion for that. Maybe some people likes to define the blockname by field without creating a preview template.
Hm. 
The solution where so simple: the label prop does the magic.
If someone needs help for this: Showing block field info as label