Input Data into another file

I have a CSV file (input.csv) containing 50k records with two empty lines seperating every 2K records. I'm looking for a way to insert this data into another CSV file (output) in the 13th column starting on row 5.


Example:

cat input.csv
2000 (1st 2K records)
\n
\n
2000 (2nd 2K records)
\n
\n
2000 (3d 2k records)
etc

The total number of actual records excluding empty lines is 50k. The Data which I need to replace in column 13th in (output.csv) file starts on row 5 and ends on row 50052.

Thank you