It will be very useful if we could add 'Date Modified' as a field when we import the data with 'Batch Append File'. Then, we can use this field to define the updated value if there has the same content in many files.
We have now added "Add date modified field" as an option to the batch append block. This will be available in 2.8 once it has been released, which should be very shortly.
In the meantime you should be able to achieve the same result by appending a "File metadata" block and a "Batch append files" block.