Sometimes I just want to change a default icon (e.g. for a folder) in OSX. So where to do this? First you need a source image to copy. These day just about every image you can preview can be used, as well as other Application or Document icons. It wasn’t always so.
Step 1: Choose a Boring Folder That Needs a New Icon
Say for instance we want to use the Blender icon for the folder it occupies in our Applications folder. The default is the boring blue folder.
Step 2: Find the Image You Would Like to Use Instead
I enter the Blender folder, select the actual Application and choose Command – I (Get Info) to get the Info window:
Step 3: Select and Copy the Small Icon Upper Left
The trick is now to select the small upper icon in the upper left and Command – C (Copy) it. It's actually a detailed icon.
Step 4: Change the Folder Icon
Now you select Command - I (Get Info) for the icon you want to change. Again, select the upper left small icon so it gets a selection border.
Step 5: Paste the Copied Image Over It
Command - V (Paste) now replaces the boring icon with the one of your choice.
Step 6: Voila
...a folder with a nice icon!