Which type of action modifies the transactions performed by the ProxySG?

The correct answer is defined actions. Defined actions are specifically designed to modify the transactions that pass through the ProxySG. These actions can include handling specific behaviors of web traffic, such as modifying headers, URLs, or other elements of the requests and responses. The key feature of defined actions is their configuration within the ProxySG policies, allowing administrators to establish specific rules that dictate how traffic should be altered based on predefined conditions.

In contrast, standard actions are typically built-in functionalities that serve common tasks without deep customization. While they manage user requests, they do not provide the granular manipulation that defined actions do. Custom actions are tailored scripts or rules created by administrators for unique situations but might not fit the scope of transactions modification.

Conditional actions are utilized in scenarios where specific criteria need to be met before executing an action, providing a level of flexibility but not inherently focused on modifying transactions directly. Therefore, defined actions are the best fit for the requirement of modifying transactions performed by the ProxySG.