You have a requirement to migrate the Relationship to a Customer/Account, but can't find the same in the Migration of Customers template.
Relationship meant here is the Relationship options available in the Relationship facet of the Account. Examples: Has Ship-To Party, Is Sold Through and so on.
The Relationship used in the Relationship facet is not part of Customers migration template. Instead, you can use the Migration activity - Migration of Business Partner Relationships
In case if this activity is not scoped, you can refer to the case document 2055341
KBA , LOD-CRM-EMP , Employee , How To