Ico2Folder

Designed for users who are continuously looking for ways to personalize their operating system, Ico2Folder is a lightweight and portable application that gives you the possibility to assign custom icons to frequently used folders.
This is not only a solution for beautifying your directories, but also a way to identify them easier by quickly taking a look at their icons.

Doesn't require installation

The entire program's packed in just one .exe file that can be saved anywhere on the computer or moved to a thumb drive to effortlessly launch Ico2Folder on any PC without setup.
It doesn't add new entries to the system registry. However, it creates an .ini file to remember you settings, so make sure you're running the tool from a write-protected device.

Assign custom icons to folders, drives and special directories

Once launched, you can use the built-in folder tree to explore disk directories and pick a folder whose icon you want to change. All you have to do is click an entry, then "Icon" and use the popup file browser to locate an ICO-formatted file, and click "Apply" to commit modifications.
It's also possible to change the icon of any local partition and several desktop utilities, such as My Network, Recycle Bin (separate icons for empty and full), My Documents, and My Computer. The label of Recycle Bin can be modified too.

Didn't work on Windows 10 in our tests

Although we managed to get Ico2Folder to run on Windows 10 in our tests, we failed in all our attempts to change folder icons. We kept running into the same error that said it couldn't modify the icon (the reason wasn't specified).
This must be because the program hasn't been updated for a long time and likely has compatibility issues with the latest Windows versions. On top of that, the developer doesn't mention the supported icon sizes, so we tried various combinations but had no success.