Can an Asset Book be added to a BU with existing Assets?

Hi-

We are using PS9.2.  There has been a legal merger of two Business Units, so we need to move the assets from BU#1 into BU#2.  BU#1 currently has an Asset Book that doesn't exist in BU#2 (a Corporate Book Type, called 'STEP').  The "STEP' Book values in Book #1 need to be included in BU#2.

Can we create/attach the 'STEP' Asset Book in BU#2, even though BU#2 already has assets?  If so, what 'happens' with the assets that already exist in BU#2.  Will we need to populate 0 values in the STEP Book for the existing assets?  Or if we make the STEP book 'not required' - will the existing BU#2 assets be OK as is?