Moving account dim member with extensibility from one hier to other

Hi

We have an account dimension with extensibility applied.

Say first level is Forecast where we capture 4 digit accounts. Forecast is then extended to Actual where we capture 8 digit accounts. Now the requirement is to move one of the 8 digit accounts to Forecast level. 

Is this even possible and how can we do this if yes?

Thank you,

Mikki