Multiple Update queries

Hello,

I am using a foreign data wrapper where i get a portion of my data
pre-loaded , i.e I get a set of rows before hand . So now i want to run
multiple update queries on this loaded data , write the changes to file ,
load the next set and continue with updates again.

How should i try to achieve my requirement ?? At what point in
postgres should i use the hook and change my execution ??

Thanks,
Harsha