Gisli, understand what you did and admire you for trying. I am so sorry the car reacted this way.
It is a pity that you were not able to attach your external battery directly to the i-MiEV's active (pre-contactor) HV terminals - I presume you do not have CHAdeMO?
I believe what happened the moment you turned the key back from its READY position is that the car detected what it thought was a stuck main contactor (as evidenced by the 322v still being present) and considered that a fatal flaw and disabled the car in addition to throwing an error code.
To answer your question, neither the CaniOn nor EVBatMon developers have openly tackled the issue of either reading the codes nor resetting them. You might contact Martin (me68) (developer of CaniOn), Xavier (priusfan), and zzcoopej (developer of EVBatMon) to see if they have done some behind-the-scenes work which may help you.
As far as I recall, no one has actually managed to get their hands onto an operational Mitsubishi MUT3 nor successfully managed to get a MUT3 clone to work.
I wish you all the best in this endeavour.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV