What is the equivalent of chmod 777?

Using cacls you can do this same type thing, example.

cacls myfile.txt /g everyone:f

Roughly:

icacls notepad.exe /grant Everyone:F

Note that this isn't exactly the same as deny ACL entries override allow entries, so if there are any deny ones you may need to remove them.

Generally, I honestly have to question the motives of what you are attempting to do. There should never be a reason to replace core operating system files with other ones.

You can easily associate text files with Notepad2 without replacing notepad.exe which should be the preferred way of dealing with this.

You can change the permissions from the command line via this information, although I personally find that the GUI permission controls are pretty easy to understand.

You can use it as follows:

CACLS files /e /p {USERNAME}:{PERMISSION}

Where:

• /p : Set new permission
• /e : Edit permission and kept old permission as it is i.e. edit ACL instead of replacing it.
• {USERNAME} : Name of user
• {PERMISSION} : Permission can be: R - Read W - Write C - Change (write) F - Full control