How would I have a field updated sequentially based on a defined where clause order

I want to be able to update a field sequentially based on the order that it was put in the where in ('[john2].[john2]','[john3].[john3]','[john].[john]') clause but it does not appear to update based on its associated order (see SQL below).
How would I have a field updated sequentially based on a pre-defined where clause order?

John

drop sequence temp_seq;
create temp sequence temp_seq;

update gis_field_configuration_bycube
set seq_in_grid = nextval('temp_seq')
where cube = 'Instruments' and level_unique_name in ('[john2].[john2]','[john3].[john3]','[john].[john]');

Instead of adding those strings in the IN clause, take those in a cursor and run the update by passing the values from the cursor. That will definitely help.