Looking for a solution to clear column data but not the headers

We have a good number of columns perhaps 100, there are about 30 that require clearing, therefore when the csv is imported, those cleared down columns will have no data in them.

I was thinking gawk, or sed to find and replace "data" with "null" or something to that affect but we may not know all of the possible values, therefore a straight clear down of column data less the header would be more appropriate.

Any ideas would be greatly appreciated?