extra trendline on Pivot Chart
 

I know you can add extra trendlines to a pivot chart through VBA. But
can I change all of the intercepts? Basically I want to add 2
additional "trendlines" showing an acceptable range of +/- 20%. I see
that there is an intercept method/property, but this seems to only
change the initial X intercept, I want to change all of them. Any
suggestions? Is this even possible on a pivot chart?