For the Patcher is not big deal, for the launcher exe is harder. you can use ResourceHacker.exe
Open your Thor.exe with the program
Open the "icon Group" Right click in the MAINICO option amd select "Replace Icon..."
Select "Open file with new Icon..." and select your best icon, I can recomend you 64x64 size
Then save your change in "Save as" option
And that's it, let me know if you have any question,
resource_hacker.zip