How to get write access to explorer.exe ?

I need to make some changes to explorer.exe file code, I end the process in task manager then open a hex editor (via task manager) and try to edit explorer.exe. I get a write access denied error.

Is this file specially protected like a system file so that it can not be modified while the windows is running?

To be clear are you trying to edit explorer the file manager or explorer the system

I'm trying to edit c:\Windows\explorer.exe

File explorer as its a system file you only have read and execute rights on it. Try coping it to another location then at the new location add yourself with rights see if you can edit it then if you then test from new location