Define a dimension automatically macth two dimensions

Hello Experts,

I have 2 dimensions GL Account and Cost Center and I need to classify each combination for a group. Example:

GL Account          Cost Center          Group

780100                   4110341               Labor

780100                   4110341               Manufacturing

780290                   4110341               Others

For each GL Account + Cost Center I have one group. I just have the dimensions GL Account and Cost Center created in my Model but my user needs reports by Group.

I thought to create a new dimensios Group. One member of this dimension will be Not Defined. All data saved by Input will used this member. And I would like to have a Package that re-classify this Not Defined Group for a validade one. I could have a file with the GL Account Cost Center and the Group.

Is it possible?