You can merge the two compared units into a third unit
to create a new entity of the same type as the original two units
or merge features from one unit into the other. By default, the initial
merge (created when you start the merge) is taken from the unit on
the left side.
To take the initial merge from the right side, set
the following flag in the General section of the Diffmerge.ini file:
"ReverseDiffOrder=TRUE"