ArcMap Data Driven Pages Dynamic Feature Labels

Question

I am trying to work out a way to change between two sets of labels on a map. I have a map with zip codes that are labeled and I want to be able to output two maps: one with the zip code label (ZIP) and one with a value from a field I have joined to the data (called chrlabel). The goal is to have one map showing data for each zip code, and a second map giving the zip code as reference.

My initial attempt which I can't get working looks like this:
1) I added a second data frame to my map and add a new layer that contains two polygons with names "zip" and "chrlabel".
2) I use this frame to enable data driven pages and then I hide it behind the primary frame (I don't want to see those polygons, I just want to use them to control the data driven pages).
3) In the zip code labels I tried to write a VBScript expression like this pseudo-code:
test = "
If test = "zip" then
label = ZIP
else
label = CHRLABEL
endif

This does not work because the dynamic text does not resolve to the page name in the VBScript.
Is there some way to call the page name in VBScript so that I can make this work?

If not, is there another way to do this?
My other thought is to add another field to the layer that gets filled with a one or a zero. Then I could replace the if-then test condition with if NewField = 1.

Then I would just need to write a script that updates all the NewFields for the zipcode features when the data driven page advances to the second page. Is there a way to trigger a script (python or other) when a data driven page changes?

Thanks