Your method works great using lexical variables as well, because the perl interpreter correctly interpolates the temporary value of $foo when that temporary value is in scope.

use strict;
my $foo = "bar baz";
{
  (my $foo = $foo) =~ s/bar/quux/;
  # do something with the modified $foo
    $foo = "changed it";
    print "The temporary value of foo is $foo.\n";
}
# now the original $foo is back again
print "The original value of foo is $foo.\n";
[download]

Running under ActiveState 5.6.1 and Windows ME, the above code first returns the temporary value of "changed it" and then the original value of "bar baz".