As far as I have understood the DOFF mechanics that is technically impossible. DOFFs cannot be altered since there is a certain set of premade DOFFs that cannot change. These DOFFs get assigned to you in your roster. You cannot change the name, portrait or any other data.
The reason behind is that DOFFs take quite a lot of data to store. If you would store all data of a DOFF seperatly for every DOFF in your roster it would take at least ten times more storage space on the server than a simple number, like it is stored today.
At the moment you have:
Individual DOFF storage would be:
Name: Frederick Dinkelsen
Race: Liberated Borg Human
Potrait: #2432 (lets say there are so and so many prtraits available)
Special Power: #21
or something like that. you see, the second method has way too muich data to store.