Advice on flipping sign on large historical data set?

Summary:

I am looking for advice on flipping the sign of a very large historical data set within our application (likely many millions of blocks).

Content:

We have an inconsistency between our various planning applications (different pods) where cost data is treated as positive or negative depending on the application, and the consolidation operators in the Account hierarchy reflect as such. Our goal here is to flip the sign on all cost data in one application ("cost" defined by specific Account members). We have both a BSO cube and an ASO reporting cube in this application. I am trying to see what options would be best. From what I can see, below are my options: