Code:
$ awk -F, '$1=="3"&&$5=="229"&&$8=="990"{OFS=FS;$9="8J8"}1' testfile
1,12,2012,IF_TB001
2,12,2012,3K3
3,Z56,00000,25,229,K900,00,990,8J8, ,USD, ,0000000000,000, , , , 550000000
3,Z56,00000,53,411,W225,00,000, , ,USD,OM170,0000000000,000, , , , -550000000
4,Z56,COUNT, 4,SUM LOC, 552215541
5,COUNT, 80