For a game developer it is possible to verify downloaded content in two ways:
1) offline mode, by hddkey, game key, individual stuff,..
this is of course crackable but needs time to find these keys. and the positions where to save the signatures.
2) online mode, by an additional xbox live check
the content signature is approved online. the correct signature is saved at xbox live so you need to crack xbl in order to play with your modified content online - impossible
If you are a good cracker you can copy the dlc to an other box and resign it there or modify the content. But on xbox live your content will be declared as edited => you cant play online with it.
So if they also implemented method 2) it should be fine to play around with the content. Otherwise we have to think about to force them to an updated .xbe.
I will not support online cheating in any way, I will just achieve to copy the dlc to boxes not registered on xbl.