First, EGR or other components do not get damaged by the over boost problem.
Secondly, ECUís rarely go on any car.
The variable vanes work by directing more exhaust gasses on to the turbo wheel.
In simple terms;
Little wind condition (tick over, low rpm) = You turn your windmill into the wind to make it turn faster.
Loads of wind (higher rpm) = Once your Windmill reached full speed, you turn it away from the wind to protect it from over spinning.
On your car, this is done via vacuum.
At low RPM (tick over to around 2200 rpm), the vanes are set that the Turbo spins faster.
After 2200 to 2500 rpm, the Help of the vanes is tapered off, as the max speed of the Turbo is reached without extra exhaust flow.
Over boost comes if you still have vacuum after the 2200 rpm limit OR the vanes are stuck in the max boost position.
A boost pressure sensor in your inlet manifold measures the Turbo boost.
If the boost is to high the ECU cuts the injection of fuel to protect the engine.(Engine light comes on).
The vacuum is controlled by the VNT solenoid.
(Bolted to the slam panel, next to your bonnet catch).
The VNT is a 3 way valve,
3. vent to the surrounding air.
Once the cut-off point is reached the vacuum-in is blocked and the vacuum-out is flooded with air from the air vent.
Neutralising the existing vacuum in the pipes to the Turbo advance mechanism.
How to test;
Pull the rubber pipe from the VNT to the Turbo actuator and block it off.(Small screw or similar).
Go for a spin,
If the car pulls like normal up to around 2000 Ė 2500 rpm, that would point to stuck vanes on the Turbo.
No vacuum = fail save setting of the Turbo is vanes in park position = no extra boost.
IF the car pulls slowly up to around 2500 rpm, but comes on boost AFTER the 2500 rpm.
The car should rev now right up to the red line if pushed without the Engine light coming on.
Then this would point to the VNT as the fault.
This simple test can point you in the right direction.