Another update: I went to see a friendly Mitsu dealer and had a look at whether it would be possible to use their MUT tool to re-load the older 0009 ROM, but while technically possible the MUT update process means it removes all previous versions of ROMs once a new one was released, so there was only the one update set for an Evo X, using the 0011 ROM.
So I bit the bullet and did a bench flash - 2 hours to make the wiring loom, 10 mins to apply the original 0009 ROM. So am now ready for pump, hi-flow cat, 3 port and then apply a tune to it
One item of not - when bench flashing with latest ECUFlash, there is no option to select recovery mode. It will automatically detect the option of this based on ROM selected and ECU you are connected to, and you can then choose a recovery flash from the ECU drop down list.