Python 3.5 convert values during re-write to new csv

I have a CSV file that I am writing to another file, but in the process want to change values based on greater then or less than. For example, in column for in the new file (row 2 from the old one) I want to transform the data from a number into a word, depending on the value in the column. My actual data has more columns, and thousands of lines, not exceeding 10k lines. Example is below:

Input.csv
duck,35,35
car,100,502
baseball,200,950
gun,500,495
taco,300,300
guitar,100,700
barbie, 200,25
gum,300,19

Desired Output.csv
duck,35,35,order now
car,100,502,order next month
baseball,200,950,no order necessary
gun,500,495,order next month
taco,300,300,order next month
guitar,100,700,order next month
barbie, 200,25,order urgent
gum,300,19,order urgent

This is my code so far, but I'm having trouble with the conversion of the amount into a new value. I think I need to use enumerate, but haven't found any examples in my research of a csv conversion with this method. Please assist.

import csv

with open('INTERIM RESULTS.CSV', 'r') as source:
  rdr = csv.reader(source)
  with open('INTERIM RESULTS FIXED.CSV', 'w', newline = '') as result:
    wtr = csv.writer(result)
    for r in rdr:
      wtr.writerow( ( r[0], r[1], r[2] ) )

EDIT: Taking Anonymous' advice, I came up with the below code. The problem is that somewhere in my "if" / "elif" statments I am not able to get the correct output. Output I currenlty get is not correct, listed below. Please assist.

import  csv 
CODE0 = '25'
CODE1 = '50'
CODE2 = '500'
CODE3 = '900'

with open('input.csv', 'r')  as  source, open('output.csv', 'w')  as  result: 
    reader = csv.reader(source) 
    writer = csv.writer(result) 
    for  row in  reader: 
        val = row[2]
    if val <= CODE0: # below 25 order urgent
            writer.writerow( ( row[0], row[1], row[2], 'order urgent'))
    elif val <= CODE1: # below 50 order now
        writer.writerow( ( row[0], row[1], row[2], 'order now'))
    elif val <= CODE2: # below 500 order next month
        writer.writerow( ( row[0], row[1], row[2], 'order next month'))
    elif val < CODE3: # below 900 order next month
        writer.writerow( ( row[0], row[1], row[2], 'order next month'))
    elif val >= CODE3: #over 900 no order necessary
        writer.writerow( ( row[0], row[1], row[2], 'no order necessary'))

Output.csv
duck,35,35,order now
car,100,502,order next month
baseball,200,950,no order necessary
gun,500,495,order now    (this is wrong, should be next month)
taco,300,300,order now    (this is wrong, should be next month)
guitar,100,700,order next month
barbie, 200,25,order urgent
gum,300,19,order urgent