Comment by jrootabega

And as a higher-level configuration you can set most, maybe even all, of the relevant invisible characters (still not sure how 0x34f grapheme joiner fits in) at once with something like:

  (custom-set-variables
   '(glyphless-char-display-control  '((format-control . hex-code)
                                       (variation-selectors . hex-code))))

This will modify values in glyphless-char-display, but it's OK to modify those directly if you need to.