Dear Akhtar,
This has been tried many times and you will generally be unable to find any useful resolution. Even the common procedure for saving variants with "U_username" does not work.
COOISPI and COOIS are run with SAP defined variants; the case of COOISPI is displayed below (SE93):
This variant SAP&COOISPI is maintained by SAP such that order header is selected (SE38):
PPIOH000 is the Order Header that comes up by default.
So, in my opinion you have the following options:
1. Save a variant with the default values that you want to have (say, the variant name is TEST).
2. Maintain a Z-transaction as shown below:
Now you will have ZCOOISPI acting just like COOISPI but taking the default variant you created.
I have not used the BAdI WORKORDER_INFOSYSTEM till date, maybe the method AT_SELECTION_SCREEN may be helpful. Take help from a technical person regarding this BAdI.
Also check note 434123 for FAQ's.
Best Regards,
Rajen