First, it should not break anything: according to tmux's ChangeLog, then tmux
support for bracketed-paste mode dates back to 1.7.
Then, on my (tmux 2.1) system, WrapForTmux actually makes the char codes be
ignored, and a tmux error file is written. I couldn't find a trace in tmux's
ChangeLog as to when this occured, and so went with switching on the major tmux
version.
The mappings are already in place, but are unused without this change.
In command line mode the escape sequences are mapped to <nop>, so they
will be ignored and keeping bracketed paste enabled all the time should
cause no trouble.
From the original author:
"Note that this only enables bracketed paste mode when the $TERM value
starts with "xterm".. you could omit the test altogether, since it
isn’t strictly necessary—it’s just trying to be careful not to do
something that might be incompatible with some other terminal type."
(http://stackoverflow.com/questions/5585129/pasting-code-into-terminal-window-into-vim-on-mac-os-x/7053522#7053522)
Since we don't understand yet if this is a problem, I recommend dropping
the check and seeing if it comes back to bite us. Should be safe since
vim has undo.
(My machine has term set to 'linux', and I'm reluctant to keep adding
clauses to that check.)