couple newb questions - reverse polarity to bridge crown xls 402 and hig pass filter?

I'd like to use my spare crown xls 402 amp. It's bridgeable but since it's the older model and doesn't have a simple switch to switch it to bridge mono mode, I have to use a y splitter and reverse the polarity into input 2. Where or how can I reverse the polarity on 3 pin XLR cable? I believe pin 1 is cold, pin 2 is hot, pin 3 is shield.

1. Can I just cut it open and reverse the wires to pin 1 and 2 and leave pin 3 alone?

2. Also, when I model in WIN ISD Pro of a TC db 500 at 3.5 ft cubed and 23 hz, the cone excursion goes way past 20 mm below 19 hz. Do I need to implement a high pass filter? When ever I do a sealed config some drivers go way up to 50 mm of excursion feeding it 1000 watts (this includes the TC3000) Am I modeling this wrong?

3. If I go sealed, what's the most I can bump up 20 hz using a BFD. Obviously I can stack the filters, but what's overkill and not safe here?

Thanks,
Thomas

I don't have my XLR cables in front of me, but are the pins labeled?

Thanks,
Thomas