I want to use .tsvx file extension for files in tab-delimited format but with extra things a frozen top row or bold, but Calc seems to just like to save in whatever formats are in the list and I’m having trouble saving/opening these kinds of files without something getting mangled.
Is there a way I can register that file extension and have it save/open (in whatever format works with tab-delimited and extra features) without things changing unexpectedly?