I cannot think of a way of doing adding such a feature. The spell check engine uses only these two files, the .dic which is a word list, and the .aff which is a special language rules syntax file. There isn’t a third file type which would essentially say, ignore some of the words I put into .dic. A curator simply wouldn’t add those words if they are not supposed to be the dictionary.
Or in other words, these data files are designed for maintainers, not users, really.
But don’t we all try to avoid using certain words in our writing? Or at least, to be very deliberate about when we use them?
I would submit there are far better ways of doing that in particular, than mucking around with the spell check dictionaries. Unlike Word, this is a program for writers. 
What was the only workaround you had back then needn’t be carried over into a program that can dynamically highlight words for any particular reason—such as not wanting to overuse them. With this method you can tweak the hot-word list as you go, rather than having to shut down, pull out plain-text editors and edit buried files in the installer, reload… Just open the search field and type in the new word to avoid!
But if you wish to use this method, it needn’t be thought of as risky, in my opinion. Just keep the original zipped and in a safe spot, and you can easily restore the vanilla settings. Worst case you can delete the modified folder and then use the UI to download it off our servers again.