There is a trick:
- Create a new empty row
- Fill in the cells for the columns that you want to rename (e.g. copy-paste to those cells)
- Right click -> Use as column headers — will apply the whole row as column names wherever a cell is not blank.
P.S. And to copy column names, you can just select the columns you need in Coda, copy them, paste to any text editor (e.g. Notepad), and then just select and copy the first row that will have column names, tab-separated. Those will be insertable in Coda cells.