As for what ive tweeked, well its quite extensive, but none of it exactly throws off game balance. In some areas its harder then stock GW, in others its a bit easier. Ive done tweeking to hedgehog and depthcharge decent rates (to match my own research), removed reloads from some uboats, and added to others, ive also messed with the damage system a bit (which ill revert if the new damage system in the next version of GW agrees with me). Ive also done other stuff like increase stock wave heights (which makes things harder in a bad storm), alterd the 24 hour crew so its a bit less anoying, changed some of the torpedo loadouts (mainly to get rid of some of the torps i dislike), I also uped the reload speed to match my data on reload speed (and i pretty much never rapid fire more then 20 rounds with out a long pause to assess damage and move more ammo up), plus a pile of other ones i dont remember, or arnt worth mentioning
All of my own tweeks are generaly small ones
And none of them are cheat ones (i honestly dont see the point even in private play). Just my interpretation of what is realistic.