Just had a look at mine and it would be dead easy, yours being slightly later has the security shield I guess ("g" below)
If you can get a hacksaw blade on the head you may be able to cut a slot like a screw head and simply undo with a screw driver, failing that cut a slot and use hammer and old screwdriver like a chisel to try and tap it undone.
Theres a very slim chance that a couple of taps on the head of screws with hammer will loosen them - rare it works but could be worth a try.
If above fails your looking at drilling or grinding heads off - drill could be unlikely due to access but something like a dremel with a grindstone in it or even a little grindstone in a drill, something like this (wear goggles though!)
Whereabouts are you - someone may be able to give a hand.
To just change over ecu for now I guess you could cut the security shield as below and just cable tie / tape new ecu to old one for now, gives you a chance to get stuff together to do proper job.
