• Disregarding suggestions to add relevant new keywords
• Adding Customer Match lists that contain data more than 90 days old
• Adding more phrase and exact match keywords in order to improve reach
• Removing negative keywords that could block relevant traffic

The correct answer is: Removing negative keywords that could block relevant traffic

Explanation: When a digital marketing manager upgrades keywords to broad match, one critical behavior to integrate into their regular optimization is the removal of negative keywords that could obstruct relevant traffic. Negative keywords can prevent eligible queries from triggering ads, potentially reducing unwanted traffic. However, when used excessively, they can limit the reach of campaigns and obstruct relevant searches that have not been considered previously.