#!/bin/bash
s=") extent size 256 next size 512 lock mode row;
) extent size 512 next size 512 lock mode row;
) extent size 256 next size 512 lock mode row;
) extent size 512 next size 512 lock mode row;
) extent size 256 next size 512 lock mode row;
) extent size 512 next size 512 lock mode row;
) extent size 512000 next size 48 lock mode row;
) extent size 512 next size 512 lock mode row;";
val=16;
sed "/extent size/{s/[0-9]\{1,\}/$val/g}" <<< "$s"