Hi @Balachandran Kannan ,
Thanks for using Microsoft Q&A !!
No, it is not possible to use the source column values in dynamic expression while adding an additional column in copy data activity. If your source is SQL then you can use Stored Procedure or SQL Query in source to add a new column and target it to the sink tables. In your case as the source is different, you could try to use Dataflow to achieve the same.
Please let me know if you have any additional questions.
Thanks
Saurabh