Thwart LZMA2 compression
Python, score = 120

import sys,hashlib
i=0
for c in sys.stdin.read():sys.stdout.write(chr(ord(c)^ord(hashlib.md5(str(i)).digest()[0])));i+=1


Makes a one-time pad using md5 in counter mode.  xors the file with it.  This has the advantage that the original and disrupted files are the same size, and that the disruptor and fixer are the same program.

The compressed disrupted files are larger than the originals.