There's a few things you can do with configuration packages.
1. Delete the data: Only possible to delete all records in a table using the "Delete" checkbox. This will not let you conditionally delete records and validation will also be enabled. I only recommend using this toggle in very limited scenarios, usually for transactional data.
2. You can overwrite data by keeping the Primary key for that table the same. See example below:
I have a list of vendors and if I inspect the page I can see the primary key is No.:
If I export a configuration package I can change all the values but keep that No. field as the value in that table, below ive changed the Name and Address:
In my vendor list you can see the name has been changed, the data has been overwritten:
3. You can also create new records using a configuration package but it needs to be for a new Primary Key that doesn't exist in that table yet. In my vendor example above i'd have to enter a number that doesn't currently exist. Some tables also have restricted no.s and they need to make a defined number series.
Hopefully that helps!