If you use HTML::TokeParser::Simple, just pass a reference to the variable to the constructor.

use HTML::TokeParser::Simple;
my $parser = HTML::TokeParser::Simple->new(\$html);

my $new_html = '';
while (my $token = $parser->get_token) {
    my $text = $token->as_is;
    $new_html .= $token->is_text ? munge_text($text) : $text;
}
print $new_html;

sub munge_text {
    # put your text munging stuff here
}
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Cheers,
Ovid

New address of my CGI Course.
Looking for work. Here's my resume. Will work for food (plus salary).