Have you ever felt the need to rename macOS to whatever you like? Like, suppose you've just adopted a dog and you're wondering: “Wouldn't it be cool if I called my OS "dogOS"?”. Well, Today, I'm here to make your dreams come true.

The first step will actually be to download the necessary files. We'll need optool and iHex.

Next, go to the desktop and make two new folders, 'Originals' and 'Modified', then put optool into 'Modified'.

Go to /Applications/Utilities/System Information.app/Contents/MacOS and copy the System Information binary into both of those folders (the "Original" folder will serve as backup, so make sure to NOT ever lose that).

Open Terminal, then run cd ~/Desktop/Modified and run ./optool strip -w -t System\ Information to strip the code signature (this is needed to run the binary, as macOS refuses to open binaries signed with a wrong certificate).

Open the System Information file in iHex, use ⌘F and switch to "Text" mode to find the macOS <version name> (replace <version name> with your version's official name, note that it is case-sensitive). Replace it with what you want, as long as it's the same length as before (spaces do count, so assume that you're on Mojave, your total string would need to be 12 in length). Look for just macOS and change the instance of 'macOS' that comes up near OS_VERSION_BUILD to match with the first part of the string you changed earlier (I did macOS -> samOS). Don't forget to save (Depending on the system configuration it may or may not ask for a password).

Now copy this modified System Information binary to /Applications/Utilities/System Information.app/Contents/MacOS and then enter your password to finalize the process.

Once you do that, the only thing that's left to do is see if it works! Open the About this Mac menu ( > About this Mac) and watch magic happen under your eyes (you may have to ⌘Q it and retry). If it didn't work, make sure you followed every step correctly (in every case you can restart the process by restoring the backup). Ok, for this post it's all, I hope to see you in the next one! See ya!