It depends on what you mean. I can't think of a standard markup for de-emphasis. You could imply it with color perhaps, e.g. some shade of grey, or size by making it smaller. At least for LaTex/HTML, both of those can be done. You would either need to use something like a macro, or a link for something like that I think. I made a link for colorized text once (
https://kitchingroup.cheme.cmu.edu/blog/2016/11/08/New-color-link-in-org-9-0-using-font-lock-to-color-the-text/) that you might be able to adapt.
John
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Professor John Kitchin (he/him/his)
Doherty Hall A207F
Department of Chemical Engineering
Carnegie Mellon University
Pittsburgh, PA 15213
412-268-7803