This is not a problem of a wrong syntax, but a problem of a wrong approach.
If you load data to dummy members you shouldn't erase them - you have to offset them. This way no matter how many times you run that script you get same result.
To implement this you have to utilize one more Dimension, usually DataSrc or Audit, and populate it with special value, say LOAD. Then script takes values from LOAD and posts opposite values to member MOVE with all other Dimensions having same members. In reports you use total of LOAD + MOVE.
This way you don't have to check amounts and keep track of what was loaded and what moved.