Cross forest migration / coexistence - distribution groups

Hi Exchange friends,
I am working on a cross forest Exchange migration project. The migration involves migrating an existing Exchange 2007 Resource forest (NWTRADERS.COM) back to the Exchange 2010 Account forest (CONTOSO.COM).

I am looking for assistance for providing synchronised distribution list membership during a co-existence phase of migrating mailboxes back into the account forest.

GALSync is currently configured between forests and a contact exists for each distribution list. However, I am ensure how to handle the distribution list membership as members are migrated. After they are migrated the mailbox in the distribution list will need to be replaced with a contact, what is the best way to handle this?

The current steps I have tested to move the Linked Mailbox back into the account forest are:

1.	Delete GALSync Contact in account forest
2.	Enable-MailUser -Identity "User1" -ExternalEmailAddress user1@contoso.com
3.	.\Prepare-MoveRequest.ps1 -Identity ‘User1’ -RemoteForestDomainController 'DC1.nwtraders.com' -RemoteForestCredential $cred -UseLocalObject –OverwriteLocalObject
4.	New-MoveRequest -Identity 'user1@nwtraders.com' -RemoteLegacy -TargetDatabase "Mailbox Database 2015386455" -RemoteGlobalCatalog 'dc1.nwtraders.com' -RemoteCredential $cred -TargetDeliveryDomain 'contoso.com
Do I need to use ADMT to migrate Linked Mailbox user to Master Account before migration? I read the blog on the Cross Forest Mailbox moves, and I am ensure if ADMT is required for moving a Linked Mailbox back in to an Acccount forest as the user account already exists. 
Also, I have found that using the -OverwriteLocalObject switch of .\PrepreMoveRequest.ps1 will copy the proxyaddresses from the LinkedMailbox back to the user account. This is what I want but is this what I should be doing?
With regard to the distribution groups, I have also tested using ADMT to migrate them, however, I am still unsure how to maintain distribution list membership during co-existence phase where members of a group may be migrated in phases.
Hopefully someone can provide some assistence,
best regards.