Question: I have a Pivot table in excel that is using a raw table as its data source. This pivot table is doing a bunch of grouping and summing of rows. 

I'd like to now use the result of this new pivot table as the data source for a new pivot table which will further modify this data. 

Is this possible with excel? I suppose you could call it 'nested pivot tables'

Answer: 
* Make your first pivot table.
* Select the first top left cell.
* Create a range name using offset:

`OFFSET(Sheet1!$A$3,0,0,COUNTA(Sheet1!$A:$A)-1,COUNTA(Sheet1!$3:$3))`
* Make your second pivot with your range name as source of data using F3.

If you change number of rows or columns from your first pivot, your second pivot will be update after refreshing pivot

GFGDT
As suggested you can change the pivot table content and paste as values.
But if you want to change the values dynamically the easiest way I found is
Go To `Insert->create pivot table`
Now in the dialog box in the input data field select the cells of your previous pivot table.