sub fix_xref {
    my ($parts, $text, $ref, $action, $link_text) = @_;
    $parts =~ s@(\d+(?:\.\d+)?(?:\([\w\d]+\))*)@<JL:ref$ref,"$action $1">s. $ref</JL>@g;
    return qq@$parts $text <JL:ref$ref,"$action">$link_text</JL>@;
}

while (<DATA>) {
    s@s\. (.+?) (of(?: the)) <JL:ref(\d+),"([^"]+)">([^<]+)</JL>@fix_xref($1,$2,$3,$4,$5)@eg;
    print;
    print "\n";
}

__DATA__
s. 3 and 4 of the <JL:ref2,"Interpretation Act">Interpretation Act</JL> 
s. 3 or 5 of the <JL:ref2,"Interpretation Act">Interpretation Act</JL> 
s. 3, 4, 5, 6, 7 or 8 of the <JL:ref2,"Interpretation Act">Interpretation Act</JL>