I don't see a way to force my first CSV column to be treated as TEXT during an IMPORT, even when that column sometimes contains data that looks like a number. A simple example of this would be a list that has 2 digit hex values from 00 to FF. The lines with A-F get treated as text, but other lines are subjected to leading zero removal.
My plan B is to import the csv file into Excel and see if classifying the column as text will preserve the data when I subsequently IMPORT the Excel file into Smartsheet.