No problem...
Lighter oil will allow the diffs to rotate easier on off power, so when you car is turning the outside wheel can turn more freely to match its different turn radius, than the inside wheel, thus helping the car turn in better.
Be sure to get Mugen oil if you can. Different brands weights vary. ie...Associate 5k oil is much heavier than Mugen 5K. Plus you'll be able to work with starting point from your manual if you use the same brand.