I have a 101 pound thrust Minn Kota Maxxum. I ran into some guys at Falcon who almost had there trip ruined because the cable broke. Luckily for them they had some contacts that brought them a new tolling motor. My question is how hard is it to replace the cable.I was considering buying one and keeping it as a spare in the event mine broke it may not ruin my trip fishin when Im 5.5 hours from home. Is this a reasonable idea.

They are not that hard to replace. I say they because there are two of them and they are different legenths so you would have to get both to be safe.To replace them all you have to do is remove the top cover to get to the top side and the bottom of the foot pedel for the other end.

You would need both cables if you're going to use them as spares. On a MinnKota, you have to remove the bottom plate of the footpedal, the top of the control box (head), pull the old cables out and run the new ones through the sheath. It's pretty straight forward. Cables are less than $20.00 each.
John