How to write to an existing excel file without overwriting data (using pandas)?

Pandas docs says it uses openpyxl for xlsx files. Quick look through the code in ExcelWriter gives a clue that something like this might work out:

import pandas
from openpyxl import load_workbook

book = load_workbook('Masterfile.xlsx')
writer = pandas.ExcelWriter('Masterfile.xlsx', engine="openpyxl") 
writer.book = book

## ExcelWriter for some reason uses writer.sheets to access the sheet.
## If you leave it empty it will not know that sheet Main is already there
## and will create a new sheet.

writer.sheets = dict((ws.title, ws) for ws in book.worksheets)

data_filtered.to_excel(writer, "Main", cols=['Diff1', 'Diff2'])

writer.save()