Can you change the Picklist value not to be the ID

Can you change the Picklist value not to be the ID

I have written a system for a client that uses a number of Lookup Dropdowns (Picklists), the picklist displayed a description but the 'Value' stored was a different column from the source.  This was done in the old version.

They client has now asked me to add some more functionality and I cannot seem to be able to replicate what I did before as the Picklist will not allow me to choose what Value is stored, it always chooses ID.

Two questions really
1. Do I now not have a choice and have to used ID's?
2. If 1 is correct, my current code continues to work but what changes will break it?

Thanks


Gordon