Chosen Solution
Upon updating to High Sierras, all but a handful of my custom desktop icons reverted to the standard blue folder icons. When I go to download new custom icons and follow the replace procedure (open, get info, copy image, paste image to replace blue folder image), this is what happens: I select “get info” and all I get is a “preview” icon. I tried copying and pasting that, but if I do, the “preview” icon becomes my folder’s image. I have no idea why this has happened, nor how to fix it. Any suggestions?
In the older OS9 we often needed to rebuild the desktop as the data structure between the icon & application/data file ID would get messed up as they where held in different structures. In OS-X & MacOS there is no means to rebuild the icon to file association as the data file is now one structure. Sadly I suspect your drive has some issues! So what to do?? First make a proper backup using TimeMachine (we don’t want a image clone). Next create if you don’t have one an external bootable drive a USB thumb drive will work. A bootable OS installer drive will also work as you may need to re-install a fresh OS. Follow this guide: How to create a bootable macOS High Sierra installer drive I might add if you have a SATA SSD drive I would recommend you stick with MacOS Sierra as Apple’s new APFS has issues with SATA based SSD’s (remember High Sierra forces you to upgrade to APFS) OK, You now have the bootable drive Boot up with it and then run Disk Utility from it. Don’t use the onboard recovery services diagnostics as it can’t alter the deeper levels of the drive. If the drive can’t be saved you’ll need to reformat it and install a fresh copy of OS.
