As far as UK cable is concerned there is no functional difference between Rom10 & Rom11 cards. You should be able to use either without problem. Just use the correct image for the card (the image layout is identical but because the ROM11 code is slightly different the bugcatchers etc all have different addresses)
Which keys are you changing ?
If you change the Emm keys then the card can't decrypt the Emm messages so it can't AU.