I know this solution comes very late, but I responded to a request on how to change the built-in Calendar icon in macOS Big Sur, macOS Monterey, macOS Ventura, macOS Sonoma
I wanted to in addition to my comment elsewhere help people with a standalone posting about the topic.
Ready? Okay, Let's go. Wait.. before we get too far along I'd like to write a disclaimer for my own good.
I HOPE THAT YOU KNOW THAT I'M NOT ATTEMPTING TO DAMAGE YOUR MACOS BIG SUR, MACOS MONTEREY, VENTURA OR SONOMA SETUP I HAVE TRIED THIS METHOD OF CHANGING OF ICONS AND THEME FILES MANY TIMES AND I CONSIDER MYSELF QUITE KNOWLEDGEABLE WHEN IT COMES TO THEMING MACOS AS I'VE MADE QUITE A FEW ALTERATIONS FOR VARIOUS ITERATIONS OF MACOS - DATING BACK TO AT LEAST MAC OS X LION. WITH OS X MAVERICKS I MADE A WHOLE SLEW OF FLAVOURS THEMES AND I'VE CONTINUED MAKING THEMES, CURSORS AND OTHER ITEMS FOR MACOS SINCE THEN
with love, Allan Nyholm Nielsen https://www.deviantart.com/allannyholm/gallery/
Download the code here and also get a Calendar icon made by me.
In the recovery Terminal window type - one at a time
csrutil disable
&
csrutil authenticated-root disable
REBOOT to the macOS Big Sur desktop
shutdown -r now
Next hold down the power button for a few seconds. On a Mac mini you'll see the front power light dim a little. You should now let go of the power button
In the recovery Terminal window type - one at a time
csrutil disable
Enter user password. Wait a little while.
Next enter
csrutil authenticated-root disable
Again, enter your user password. Wait a little while. Reboot.
My experience: You'll be required to enter your user password for both these operations when on an Apple Silicon Mac. And you also have to have macOS user already set up
I urge you to read up on the entry this ThemeEngine fork by Jeremy Legendre that explains how to change theme files on modern macOS’ like Big Sur and macOS Monterey. It's really the only option at this point.
Outgoing link to readme https://github.com/jslegendre/ThemeEngine#readme
Download latest compatible version for macOS Sonoma. Version 118 at this writing.
/System/Library/PrivateFrameworks/CalendarUIKit.framework/Versions/A/Resources/App-empty.icns
You can only change this icon after opening up the system by means explained in the link above. Basically you change the icon in the newly made location that you’ve set up.
Be aware that you’ll be required to both locate and change the icon in this path, not via the top level Mac drive structure, but from the newly made directory where you from now on will change ALL YOUR SYSTEM FILES for the purpose of changing the Calendar and system level theme files.
Remember to use the bless command after you’re done - again described great by Jeremy Legendre in his readme)
Reboot your Mac while in the Terminal
sudo shutdown -r now
- Create a directory in your Home directory with a name that will make sense for your theming efforts. In this example I call the directory 'livemount'
- Open Terminal
- Type in
mount - Find the top-most drive listed e.g disk2s5s1 this is something different for most users
- Type
sudo mount -o nobrowse -t apfs /dev/disk2s5 /Users/yourusernamehere/livemount/
notice the last entry of the disk name is missing in the disk name above: s1
- Navigate to
/Users/yourusernamehere/livemount/ - Now you ought to see your system disk mounted in this folder
- Navigate to
/System/Library/PrivateFrameworks/CalendarUIKit.framework/Versions/A/Resources/in that system disk within that folder you made called livemount - Change the App-Empty.icns file
- Type
sudo bless --mount /Users/yourusernamehere/livemount/ --bootefi --create-snapshot - Wait a second or 2 for the blessing of your system disk to complete
- Type
sudo shutdown -r now - Alternatively you can use the Finder - Restart... menu item.
- Your Mac reboots
- The exact same process as mentioned earlier
- This time instead you'll want to change the Calendar icon inside
/System/Applications/Calendar/Contents/Resources/Assets.car - You will need ThemeEngine to change the icons in here as it can edit and save out the
.carfile you need. - Best practice for changing system files is to always make backups!
- When you're using an Apple Silicon Mac you'll need to change the bless command a little. If all you're doing is changing the Calendar icon on the Dock you can settle for only blessing the framework.
sudo bless --mount "$HOME/livemount/System/Library/PrivateFrameworks/CalendarUIKit.framework/" --setBoot --create-snapshot
Jeremy Legendre Has made it possible to continue low-level system theming past macOS Big Sur https://github.com/jslegendre https://github.com/jslegendre/ThemeEngine/releases
Alex Zielenski One of my earlier partners in theming - Maker of Mousecape and ThemeEngine https://github.com/alexzielenski/
Wolfgang Baird MacForge & PaintCan plugin https://github.com/w0lfschild
The path to the icon is courtesy of Paulo Freitas Valvator over at MacRumors Forums here: https://forums.macrumors.com/threads/changing-system-icons-on-big-sur.2243470/page-4?post=29648053#post-29648053
Paulo explains in the thread linked to, that you need to change the icon in the Assets.car in 2 places on your system. However, my experience is that I only needed to change the actual ICNS file as in indicated in the Finder path above as I could not locate the icns file inside the Assets.car file.