Processing Change in Entity Type for Self-Directed Solo 401k

I have a CPA firm that is currently structured as an LLC that wants to open up a
Self-Directed Solo 401k.
 

In approximately a year, they will be setting up another entity—a Corporation,
which will be a new legal entity in addition to their LLC. Note that the CPA firm only has two owners (husband and wife) and no full-time employees.
 

If they want to fund (make Solo 401k contributions from self-employment compensation) their solo 401k in 2013  from their new Corporation, do we have to terminate their old Self-Directed Solo plan and open a new Solo 401k or do we amend the old Self-Directed Solo 401k plan with the new company name, and establish a new EIN for the Solo 401k.

No elaborate change is required. Your Solo 401k provider will simply need to update the Solo 401k plan document to reflect the new entity (the Corporation) and submit letter to the IRS to communicate to them the new company associated with the Self-Directed Solo 401k.  

Therefore, the EIN will remain the same and the same Solo 401k account tile remains the same. Solo 401k providers generally don’t charge a fee for processing this type of Solo 401k administrative update nor does the filing of a final Form 5500-EZ apply since you are not terminating the Solo 401k plan, but just simply updating the entity type associated with with it.