Hi!
SH3 loads the version from gamefolder\data\cfg into "YourDocuments"\SH3\cfg and then uses the version in "YourDocuments"
If you want to effect an immediate change, change
both (that way when SH3 loads from gamefolder in the future you won't revert to the original.
REMEMBER TO MAKE A BACKUP COPY OF THE FILE FIRST! 
Pablo
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"...far better it is to dare mighty things, to win glorious triumphs even though checkered by failure, than to rank with those poor spirits who neither enjoy much nor suffer much, because they live in the gray twilight that knows neither victory nor defeat."
- Theodore Roosevelt,
speech before the Hamilton Club, Chicago, April 10, 1899