Brother Exemption is to carried Forward upto 3 attempts after securing in an attempt.
And looking onto your case, thats not the practice of the institute at all.
GRP I marks[dec'12] can not be set off against GRP II marks[jun'13].
But the exemption in any subject( if any) in the december 2012 can be forwarded to next successive attempt. i.e., june2013
so, as you have scored 141 in grp I this time, if you have scored an exemeption[60+marks] in any subject, that can be carried forward to your june 2013 attempt. that paper you wont have to give it again.
and you wish to appear only a group II this time, then getting an exemption in that will benefit the next succesive attempt, but combination of group wise marks are not allowd here.
. And yes, you have to separately pass the frst group..scoring very good marks in GRP II june attempt will also not be considered as both groups passed.
My suggestion would be that
1.Apply for verification of your all papers of GRP I.
2. Fill the Exam form for grp I and Grp II [both] this time.
3.Start preparing for the june 2013 exams
Regards.