I just put an older set of avid juicy 7s that I had laying around on my karate monkey and found out the hoses are too short. I was wondering if I could get away with reusing the rear line on the front, and then I would only have to buy one new line to replace the line that was on the rear. I know from working on motorcycles and cars that you should never reuse brake lines but I feel like it might not be as big a deal on a bicycle.

It will work fine, but you will need a new hose barb and olive for the end that you will have to cut to length.