However, that said, there are some antenna systems that are actually tuned to include "the half mile of cable" as part of the whole system... so you might be detuning your antenna by not including the cable.

The other issue is that barrels can be lossy... I think it is a 3 db loss for a barrel (if I remember right), which to a GPS signal is a big thing (GPS is already "down in the dirt" at about -150dbm)

Your safest bet is to remove or cut off the connector, pass the cable through the space and then solder one new connector back on the end, properly dressing the cable for the connector. Since this is a GPS cable, I am somewhat inclined to think you can probably shorten the cable too and it won't hurt.

Forget the idea of splicing... at GPS frequencies, a splice is just not nice.