Is there any way to increase this? I don't think so, since I went ahead and tried a skirmish, and no matter how many more LR sensors I added, it seems to cap at 100.

Is there a config file somewhere that can change this? (not for the campaign, but I'd like to make some epic fleets....

You change it before you start the match, in the lobby there's a slider on the top left that goes up to 300.

But it is possible if you have the game to version 1.7.
Conquest: Frontier Wars patch 1.07 can be downloaded here: http://www.moddb.com/games/conquest-frontier-wars1/downloads/conquest-frontier-wars-patch-107
Or download the already patched version of the game here: https://yadi.sk/d/FI9bpGKUYgYKD

The game is already patched to 1.07 and please don't share illegal download links for the game.

Don't see anything illegal there (by european copyright standards anyway)

Distributing the full game is of course illegal and isn't tolerated by GOG.