Merge stage: Link Ordering
The link ordering section on the Stage tab allows you to specify which of the input links is the master link and the order in which links input to the Merge stage are processed.
You can also specify which of the output links is the master link, and which of the reject links corresponds to which of the incoming update links.
By default the links will be processed in the order they were added. To rearrange them, choose an input link and click the up arrow button or the down arrow button.