If the field is not added to the page layout when you want to create the records for the custom metadata by using manage record button then you will not be able to see that field in the layout.
Edit or create record page:
This can also be done directly in the SFDX.
You just need to create an additional metadata file in the object folder:
<?xml version="1.0" encoding="UTF-8"?>
A quick approach that can be followed is instead of metadata, you can create a FieldSet, lets say "Copy Attribute Fields" Field Set on Order object (assuming that Order is source and Order Line Item is target). Now using the field set you can determine at run time which attributes needs to be copied on the target object, at this point of time make ...