What should be done if a Developer needs to modify configuration settings in Sitecore that can't be patched?

Utilizing an XDT transform file is the appropriate approach for modifying configuration settings in Sitecore that cannot be patched. XDT (XML Document Transform) is used to apply transformations to configuration files during deployment. This is particularly useful when dealing with settings that may not allow for standard patching methods, enabling developers to ensure their configurations are tailored to their specific environments or needs.

When using an XDT transform, developers can specify exactly how they want to alter elements within the configuration files, managing changes seamlessly without manual edits that could lead to errors or inconsistencies. This ensures that any overrides or modifications are consistent across different environments and deployments.

In contrast, using the Sitecore control panel primarily assists with administrative tasks and user functions rather than deep configuration changes. Consulting Sitecore documentation can provide guidance and best practices but does not directly address the need to modify configuration files that cannot be patched, making it less practical as a solution in this specific scenario. Hence, the most effective method for this situation is indeed employing an XDT transform file.