I did a splice of a cat5 data cable when a control room was moved, many years ago. It was just a simple untwist the pair for a half-inch, strip and tightly twist the wires , and trim back down to a quarter inch of tightly twisted, and then just a small bit of solder very quickly done so as to not melt-back the insulation. It has been working for almost 20 years, no problems yet. But that is a long run, about 200 feet through steel conduit, with plastic conduit for the underground portion below a parking lot. I doubt that they use it for hi-def full motion movies, only text data and emails.
So the religious fanatisism about cabling may be a bit in excess, it seems.
And once again, slowing down a bit can work wonders.
One more thing is that nobody would ever use Cat5 cable for an RS232 link. Plus, RS232 has a number of speeds available, from a slow 300 baud up to at least 19.2 KILO-baud.

 

On RS232 as speed goes up distance goes down significantly. @19.2 you are limited to ~50 feet. Hence modems...

 

On RS232 as speed goes up distance goes down significantly. @19.2 you are limited to ~50 feet. Hence modems...

That was my point exactly!!!

 

Why not just add a switch? They're cheap and -- as a side benefit -- you get some additional ports (i.e. future proof).

https://www.google.com/shopping/product/6264736427991128676