Custom rules allow you to apply business rules to your feeds to change field attributes, add third-party tracking, replace text in your data, calculate number values and generally improve feed quality.

To append UTM parameters to product URLs:

1. Go to the Feeds tab in the left navigation 
2. Select the desired feed template
3. Select Custom rules under the SETUP section of the sidebar menu
4. Click the plus button 
5. Name your rule
6. Under SET, select the feed field you want to change
7. Under TO, select your product URL field (this should be a Product [P] field) from the drop-down menu
8. In the next available field, type in your UTM parameters
9. Enter the conditions for this rule. To add additional conditions, click the Condition icon.
10. Save
    

    To save this new custom rule as a Global Rule, click the global rule dop-down option and select Save as new global rule.