If the way you make something depends on how many you are going to make, you can define them all as choices and get the planning system to choose the appropriate one. To do this, define each method choice as an assembly, then use each as a part choice in the main method, e.g.

ASSEMBLY small batch
 STEP 1
 STEP 2
 ...
ASSEMBLY big batch
 STEP 1
 ...
METHOD
 STEP 1
         PART Assembly small batch
                 PART(alt) Assembly big batch
         ...
 STEP 2
 ...

The planning system will evaluate both the small batch and big batch options and choose the best for the situation. This technique also works using DO records in place of PART records.