Thanks, for that information. Since I have no coding knowlege I reached out to stackexchange for some help for a workaround. Question is here: https://emacs.stackexchange.com/questions/35626/how-to-make-my-own-org-mode-text-emphasis-work-again 
One guy mentioned this after I wrote about this bug report:

"If they don't want items added to org-emphasis-alist they shouldn't use the repeat customization type which allows insertion and deletion. Furthermore, they should add a note about this restriction in the doc string of org-emphasis-alist. Maybe, you can give a follow-up in the bug-report about that."

So I did what he requested. He also provided me with a working solution. Even with that said I might ask if you could consider supporting adding new emphasis definitions in the future? For people like me who are not able to write a function to solve the problem in an instant this customize option is like the red carpet already lying on the floor.

With kind regards,
Jens Lange

2017-09-19 21:23 GMT+02:00 Nicolas Goaziou <mail@nicolasgoaziou.fr>:
Jens Lange <jens.lange.de@gmail.com> writes:

> Hmm, but that worked until recently. Without any hook.
>
> Or was your answer like: Good for you that it worked in the past but since
> it ain't supported we won't make it work again?

That's more like it, sorry. The fact that it worked doesn't mean it was
supported.

As I suggested there are other ways to achieve what you want.

Regards,



--
Mit freundlichen Grüssen / With kind regards:
Jens Lange