I was wondering if I could use a DB9 RS232 Serial Splitter Cable like this 12" DB9 RS232 Serial Splitter Cable, 1 Male / 2 Female

and have the PA (I have mine set to switch to detect mode only, I'm in California and may need to do that if ever pulled over) plugged into to "A" of side leaving "B" side blank.

Then when I needed to update unplug the PA and plug in my USB to serial adapter into "B" side ?

Any other way to do this (I've seen post on A/B switch but space is limited)?