Thanks, here attached is a patch doing that.
Anything else that patch should contain? I remember the commit message is supposed to contain the list of modified files.
I noticed a problem: I can customize the unicode char just fine, but whenever I try to customize the glyphless char and use `emacs -nw` it doesn't work, it still uses "^" or "v".
Okay I found that it works if I re-eval the whole `defvar tabulated-list-glyphless-char-display`, but not if I `eval-buffer` the whole buffer. I cannot understand why. I guess that `eval-buffer` triggers the loading of `tabulated-list.elc`, which resets the table to its default value.
Also I was wondering if this:
(let ((table (make-char-table 'glyphless-char-display nil)))
Should `make-char-table` purpose really be 'glyphless-char-display? I'm not familiar enough with it, but I was wondering if it could clash with the real `glyphless-char-display` variable purpose.