Duplicating any column as a "Custom Column" allows the editing of the values in that column.
As example, to alter the dates for a set of documents right-click on the DATE column header and select Duplicate as Custom Column. This will create a new column called DATE_CUSTOM.
The values in the DATE_CUSTOM column can be changed by double clicking a specific cell. This double click action will make the cell editable AND bring up the document browser. Click on the drop down arrow to bring up a calendar to use to choose a date.
To change the name of Custom Columns under Settings-Edit Columns.
Note: Duplicating a column as a Custom Column duplicates ALL of the values in the source column for the entire database, not just for the records currently in your filtered result set.