First it depends on whether or not you are crafting a legal document. If it is not a legal document, you need only put the new word in parenthesis and then use the short version for the rest of the document.
For more formal needs, henceforth is a reference to time so it is less precise than the term hereinafter, which specifies the current document.
Benjamin P.
tutor
Hereafter, when used as an adverb (something that modifies an action word) means exactly the same thing as henceforth. It's a reference to time--from this moment onward. When used as a noun, a thing, it does as you say, refer only to the afterlife. But the term hereinafter means here within the remainder of this document.
Report
11/21/20
Neil M.
A mention of "hereafter" vs "hereinafter" would be useful. I always associate the former with the afterlife...11/21/20