My CT ratio was 100/5, but it should have been 120/5.
I'm looking for a way to modify my readings to reflect the correct CT ratio.

You can fix the profile data.
You will need to know:
-from which date to which date the data is wrong.
-the wrong (old) CT ratio (e.g. 100/5)
-the correct (new) CT ratio (e.g. 120/5)
Firstly, we need to determine the multiplier.
To do this we divide the new CT ratio by the old CT ratio.
A CT ratio can also be represented as a value.
Just divide the first number with the second number.
e.g. For the CT ratio 100/5: 100 / 5 = 20
For the CT ratio 120/5: 100 / 5 = 24
Now, to get the multiplier, divide the new CT value by the old CT value:
e.g. 24 / 20 = 1.2
Navigate to your meter, then under Tools->Modify Readings
Enter the From Date and Time
Enter the To Date and Time
Enter the multiplier
Click on Submit Query

http://wiki.pnpscada.com/CT_Multiplier_Calculator.html