Swapping an Auto transmission to Sequential required changing to MT ecu?

[speedjet]

Hello,

I have a S550 Mustang GT with 6r80 that I'm considering to swap my transmission out to a Sequential transmission or a close ratio MT gearbox for track only.
All the engine tune was good and I was not thinking to change my ecu to a standalone type ecu and start from zero.

Is it possible to retain the stock ECU and disable the auto transmission?

Or I must get the Ford racing Control pack ecu set to get this done?

[veeefour]

The OFF (ECM 45820) switch for AT is there but I have never tried this method.