Over ride CV cell amount

Hello & Happy Friday.

How do I over-ride a cube view cell amount? For example: IF an account (for e.g. Fleet Revenue %) is less than a certain number (for e.g. 45%), then run a custom calculation in all those cell. Else, show the original number.

The excel-sheet uses an IF statement as shown below. I'm thinking that I have to write a BR (with nested IF) to run this. Will be great if there is a existing BR or method somewhere else, that I can reference.

Any ideas/suggestions will be appreciated. Thank you!