In the old xaml TFS build era there was an option which seemed to have disappeared with the arrival of the new build architecture: cleaning sources at queue time without a modification to the build definition.
After queuing the build from Visual Studio you had the option to navigate to the parameters tab where you could choose on the fly your preferred method of cleaning the workspace, without forcing an upfront update to the build definition.
Now, with the new build system, the queue dialog window has changed a bit and that specific option is not available anymore out-of-the-box. The “Clean” option in the build definition also seems to be limited to a fixed true/false value from the dropdown.
Luckily, the field can also hold a custom variable which has been defined in the variables section. Don’t forget to mark the custom variable as “settable at queue time”.
Queuing a new build will now nicely provide you the option to choose the non-default value.