JavaCard OS

I have a legacy contact card (non java card). I am able to emulate the legacy card command set. Would it be possible to also change the ATR of my javacard to be the same as my legacy card ? From my understanding, ATR defines card communication parameters and since each chip has its own properties, does this mean this is not possible ? Thanks.

Yes, it is impossible to change ATR of javacard if you don't have its reference manual.