Yes, you can change Perl's built in variables such as $/ and $\ to suit your needs, but something tells me you would be better off solving your problem with a CPAN module instead - a solution that has been tried, tested, and proven to be to robust enough to take care of the problems you haven't addressed yet. For example, HTML::FromText does a pretty darned good job of converting plain text into HTML for you. But adding line break tags is really trivial:

$str =~ s/\r?\n?/<br\/>\n/g;
$_ =~ s/\r?\n?$/<br\/>\n/ for @array;
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Question ... did you mean a literal &lt;BR> or a <BR> tag? Either case, you really should be keeping up date with HTML standards ... lower case and close off non-nested tags: <br/>.

Please do heed dragonchild's advice and give us more information on what you are trying to do. For example, posting a good snippet of the file you are parsing would be a good start.

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)