You can only assign customer rules to customer rule packs. You cannot modify Trellix rule packs.
To add rules to a rule pack:
From the main menu, select Configure > Rules.
In the table of rules on the Rules page, select the Customer Rules tab.
Select the customer rule you would like to add to your rule pack in the table.
On the rule detail page, click the
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icon in the upper right corner of the page.In the Update Rule dialog box, select the rule pack for the rule using the drop-down menu in the Rule Pack field.
Click Update Rule.
The rule is added to the rule pack. Repeat these steps to add more rules to the rule pack.