let @x = '^ \+[1-9][0-9]\{3}-[-A-Z0-9]*. \+$'
You don't even need to load it explicitly in the vimrc,
registers are remembered by the viminfo (see ":help viminfo").
...as long as your copy of vim is
1) compiled with +viminfo
2) set to use viminfo (non-empty 'viminfo') and
3) the 'viminfo' set to remember registers (s >0)
4) the length of the saved text doesn't exceed either the kb
limit ("s") or the line-length limit ("<") of your viminfo setting
For the example at hand, #3 and #4 aren't likely to be
problematic, but #1 or #2 may. Several of my boxes have viminfo
disabled because I like to know the state of my vim rather than
try to remember which vim process I last used and what
information it saved in my viminfo. Not a big deal, but enough
to have been bothered by startup times enough to disable viminfo
on occasion.
However, as Tony says, if your viminfo is set to remember
registers, all you have to do is remember not to tromp over the
saved register, and you're good to go.
Just my $0.02
-tim
