Add customization to CKEditor for specific H5P plugin

Okay, I recently found this: https://h5p.org/adding-text-editor-buttons . I guess this could be the way to go here.

on gitter /h5p-community someone told me that I could also just generate a new ckeditor, replace it with the old one on my server and then change the semantics.json proper TAGs to allow the tags I want. What you think about this way?

Sidenote: it is currently not working ^^

Of course :) 

I´m trying since several days to allow more html tag´s in the editor, but any tries doesn´t seem to have an effect. I followed this http://docs.ckeditor.com/#!/guide/dev_acf documention.
Additional I´ve built a custom ckEditor in with the ckEditor-builder and I also changed the proper TAGs in the semantics.json of the plugin we´re using H5P.TEXT-1.1. But nothing worked so far.

Path of the config File i worked with: /h5p-resource/h5p-editor-php-library/ckeditor/config.js
I tried to disable ACF CKEDITOR.config.allowedContent = true;
I also tried to allowExtraContent config.extraAllowedContent = 'dl dt dd button';
and several other things.

So it seems that neither of my changes have an effect. The new generated editor doesn´t show up (still the old one) and the defined allowed tags are still escaped. 

Another Question:

I have tried several plugins and every plugins displays the editor with different functionallity (buttons). But I can´t find the place where this is defined. How does H5P plugins say the Editor which functionallty to show? For Example: Some include a button for making text bold and other do allow to include URL´s.