Impacted metric calculation

[guybm]

hi
I'm working on cognos 8.2
my customers in my org. demand a new action that I'm not familiar with.

Q: when one metric is calculated and influenced by other impacting metrics , the calculation is starting from the first time that we have data on and calculate the metric score.

when I'm changing one of the impacting metrics i want that my new calculation will start  from the period that i changed the impacting metric and all the old scores will remain as is, according to the old calc.

thanks in advance ,