You are correct. Importing a data source file will create input data fields (recipient schema fields) with the same name as the field headers in the first row of the data, and also ADORs or content objects with the same name.
The ADORs or content objects don't have to be the same name. You can rename them, or create new content objects with different names and add input data fields to the content object expression.
For example, you could create an ADOR named "fullname" and the expression could be |->[firstname] & " " & |->[lastname]
If you are trying to make an ADOR object refer to other ADOR objects, then this is not possible. ADORs/content objects are designed to be placed into the document (InDesign/Email/Webpage/etc)
If you want to create an expression that can be used in multiple ADOR objects, then you should use variables for this purpose.