Delta from one ODS to another due to change in update rule

Hi,

This is my scenario:

Init + delta -

> CUBE A

ODS A -

> ODS B----

>CUBE B

-

> ODS C----

>CUBE C

Delta has been initialized and is flowing every nite from the ODS A into the three Datatargets shown above(via the PSA).

Now there is a defect in the update rule of ODS A to ODS C and i have to change the update mode of all KF to addition(it was overwrite before).

I have my entire data loaded to ODS C through Overwrite mode.Now if i change the update rule to Addition,how my next delta will work and how the records will be reflected in the ODS C and further to CUBE C?

Can anyone tell me the exact proces ?

thnks in advance

Dhanya.