I would guess it has to do with "a few minor things" that you changed. *Normally* a filename error will actually pop-up an error dialog when you start OFP or simply result in a non-textured model. I've found that if it crashes on me once I'm in the map it's probably an invalid value, bad array, etc...
Of course not knowing exactly what "a few minor things" are, and having to assume that you properly changed the rate of fire and scope distance makes it a little difficult to help you solve the problem
Post your config.cpp, or at least the changed parts and someone here can give you a better answer.
Also, whenever I'm just playing around with changing values I put the original value at the end of the line in a comment (example: dispersion=0.007000; // 0.000500) that way if a problem does arise I can go back and start reverting the settings until I can isolate the problem.
Hope that helps