sub delete_nth_occurence {
    my ($rx, $str, $n) = @_;
    my @piece = split /($rx)/, $str, $n + 1;
    splice @piece, -2, 1 if @piece > 2;
    return join '', @piece;
}

print delete_nth_occurence(qr/\.0/, '123.0456.0789.0', 2);
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