Adding editable Customfields inside the Client-Area

[Nethinks]

Since the last Post on this Topic is pretty old i wanted to ask this question again:

How can i make the Custom Fields (which can be only edited on first configuration of the product) editable inside the Client Area? I know that its theoretically possible:

-> https://whmcs.community/topic/290577-make-custom-fields-in-client-area-product-details-editable/?tab=comments#comment-1303034

But this post is pretty old and the solution doesn't seem to work anymore. I am currently working of the "Provisioning Module"  (https://github.com/WHMCS/sample-provisioning-module), added a few custom fields and want to make them editable now. 

I looked trough many community posts and didn't really find anything useful besides "get someone to program it for you" and redirects to the other Post i linked above.

In case the method in said post can still be implemented today, is there any more documentation on how to do it?

Thanks c: