How to write script logic for performing calculations based on values of different members within a same dimension to update another member in the same dimension?

Hello all

Here is what I wish to calculate in my Input schedule on a run time basis:

The user can enter or change values for Customer Forecast and Price 2. Whether there is an input or not, a change in the value or not- the calculation must stay intact all the time.

The issue is that I have to juggle and compare the values for the members within the same dimension to calculate value for another member in the same dimension.

I need to know if we can write script logic for this scenario. I know we can achieve this using BADI but that is not possible for now due to time constraints.

Also, I would like to know if there is any SAP delivered Callback API for VB macro as we have in BEx and Advanced Analysis; for instance- writing a macro for the calculation but calling it based on any event happening in the particular sheet- which could be input/change/refresh/opening the template etc.

Any help would be truly appreciated!