Pivot Table Top 20 excluding specific items
 

I have a pivot table and I'd like to a) group the top 20 companies by the
amount of business they've transacted but excluding "Unspecified" and
"(blank)", and b) group the remaining companies as "Other" and include
"Unspecified" and "(blank)" in this selection.

Any ideas how I can do two separate groupings where there are some companies
that I don't want to include in the top 20?