Copy Master and SELECT child records

You could use CopyMasterDetail if you wanted by modifying the report link field(s) that you're referencing. The idea behind a normal report link is that it's matching Value from Parent to Value in Child. So in most relationship that is matching the [Record ID#] of your parent to the Related Parent field in your child. 

You could make a new field though that is something like [Conditional Parent] that is an IF statement like: 

if( Status != Completed, [Related Parent], null)

Then make a new report link that matches Record ID# from Parent to [Conditional Parent] value in child. Use that as your CopyMasterDetail relfid. The idea is that you're conditionally selecting which records you want copied in the report link