Specify exactly how you changed the data.ini entry. And between changes, did you totally get out of the program and then come back into it? Ini changes will probably not take effect until after the program is shut down and restarted.
FastCargo
PS I am assuming the method you tried was this (changes in BOLD):
[bombBay]
SystemType=WEAPON_STATION
StationID=5
StationGroupID=4
StationType=INTERNAL
AttachmentPosition=0.0,1.226,-0.586
AttachmentAngles=0.0,0.0,0.0
LoadLimit=1000
AllowedWeaponClass=BOMB,EOGB,AHM,IRM
AttachmentType=NATO,USN,USAF
NumWeapons=4
AttachmentPosition001=-0.23,1.250,-0.33
AttachmentPosition002=0.23,1.250,-0.33
AttachmentPosition003=-0.23,1.250,-0.63
AttachmentPosition004=0.23,1.250,-0.63
DeploymentMethod=OPEN_BOMBBAY_DOOR
BombBayAnimationID=8
BombBayOpenTime=1.5
BombBayCloseTime=1.5
MinExtentPosition=-0.50,1.226,-0.586
MaxExtentPosition= 0.50,1.226,-0.586