what would happen if I reflash A4TF520F over A4TF400E??

[nabilsx]

Hello guys

my friend has a 2003 WRX Manual transmition, the car got a jdm engine swap and due to that it went crazy rich, so what they did was that they replaced stock ECU with an A4TF400E and that reduced the Rich state a little bit.
so I was wondering since car already have a manual tranny, is it possible for me to reflash the A4TF400E with an A4TF520F flash? I am ready to try but afraid to not be able to reflash back to stock file if A4TF520F didn't match.
what do you guys say? should I do it?

Thanks a million
PEACE
Nabil