Modify an existing Excel file using Openpyxl in Python

Question

I am basically trying to copy some specific columns from a CSV file and paste those in an existing excel file[*.xlsx] using python. Say for example, you have a CSV file like this :

 col_1   col_2   col_3  col_4
  1        2       3     4
  5        6       7     8
  9       10      11    12 

So, i wanted to copy the both col_3 and col_4 and paste those in col_8 and col_9 in an existing excel file [which is a .XLSX format]. I have tried this in various way to solve, but could not find out the exact way. i tried something like this :

with open( read_x_csv, 'rb') as f:
    reader = csv.reader(f)
    for row in reader: 
            list1 = row[13] 
            queue1.append(list1)
            list2 = row[14] 
            queue2.append(list2)
            list3 = row[15] 
            queue3.append(list3)
            list4 = row[16] 
            queue4.append(list4)

and then

 rb = open_workbook("Exact file path.....")
 wb = copy(rb)
 ws = wb.get_sheet(0) 

 row_no = 0

 for item in queue1:
    if(item != ""):
            ii = int(item)
            ws.write(row_no,12,ii) 
            row_no = row_no + 1
            #ws.write(item)
            print item
    else:

            ws.write(row_no,12,item) 
            row_no = row_no + 1

  wb.save("Output.xls") 

but problem with this solution is it does not allow me to save as *.XLSX format which is strictly required for me.

I have tried to use Openpyxl as it can handle *.XLSX format, but could not find out a way to modify the existing excel file. can anyone please help on this?

Doubt : 1) Can we really read a whole column from a CSV file and store into an array/list using python? 2) Can we modify the existing excel file which is in .XLSX format using openpyxl or any other package?