Hi,
According to your requirement if 2 different assets are created then for 30000Rs asset you can assign the depreciation key of '0000' by which no depreciation gets posted to that asset. Kindly make sure that earleir fiscal year is closed else system will show the retrospective amount in the previous asset fiscal year 12th period.
If both amount are in single asset then post the normal depreciation amount and then post an unplanned depreciation of the reversal amount to the extent to which you don't want tot post depreciation.
Regards,
Malhar.