One option to consider is to move the replication of eVar1 to prop1 out of Launch and into processing rules.
You could set up a conditional processing rule that only sets prop1 on hits having eVar1 set.
Pro: Doing it this way cleans up the beacon. It saves a few bytes.
Con: The functionality is hidden in processing rules.
The other option is to put the logic in AA doPlugins and test for a value of evar1 before setting prop1=D=v1