We recently increased the number of lead sources we have and I wanted to clean up our opportunities (including the historical ones) to map to the new lead sources. The problem was that I didn’t want to go through over 10,000 opportunities by hand, so I figured out this little trick. We have in the opportunity record a description of the original opportunity, and inside that description we had buried the lead source. Given this information, here is what I did to get the opportunity lead source:

1. Create a filter on the description that uses “Starts With” and a wildcard % of the information you want to search for
2. Check the box for group update
3. Select all records
4. Using the drop down, select mass update
5. Replace the field you want, such as lead source