Updating using a case statement that uses 2 sets of joins (updating the same column for both sets)

Hello,

In one sql statement, I'm trying to do an update based using 2 different set of joins.  For an example, if the account number=abc123, I would find those records with 1 set of joins.  For all other accounts, the records would be found using a different set of joins.  However, in both cases the update is the same.  How would I achieve this? 

AS