\expandafter\def\expandafter\UrlBreaks\expandafter{\UrlBreaks% save the current one \do\a\do\b\do\c\do\d\do\e\do\f\do\g\do\h\do\i\do\j% \do\k\do\l\do\m\do\n\do\o\do\p\do\q\do\r\do\s\do\t% \do\u\do\v\do\w\do\x\do\y\do\z\do\A\do\B\do\C\do\D% \do\E\do\F\do\G\do\H\do\I\do\J\do\K\do\L\do\M\do\N% \do\O\do\P\do\Q\do\R\do\S\do\T\do\U\do\V\do\W\do\X% \do\Y\do\Z\do\-% \do1\do2\do3\do4\do5\do6\do7\do8\do9\do0} % feel free to add other \do<symbol> to break at other symbols