Is it possible to modify the string used to delimit output columns in command line MySQL query results? E.g. could I change
Yes. From mysql documentation:
[mysql commandline] When used interactively, query results are presented in an ASCII-table format. When used noninteractively (for example, as a filter), the result is presented in tab-separated format. The output format can be changed using command options.
Thus, you can pipe mysql commandlines output to sed and change tabs to whatever you want.
see sed doc: http://www.grymoire.com/Unix/Sed.html#uh-6
also there seems to be a patch to add that option explicitly: http://bugs.mysql.com/bug.php?id=8904