"<a href='foo'>bar</a>bla<br>bla<a href='bar'>foo</a>";

##</code><code>##

   "<a href='foo'>bar</a>blabla<a href='bar'>foo</a>";

##</code><code>##

while ($value =~ /href='\K([^']*<br>[^']*)(?=')/p) {
    my ($pre, $post) = (${^PREMATCH}, ${^POSTMATCH});
    my $href = $1;
    $href =~ s/<br>//g;
    $value = "$pre$href$post";
}