Settings > Configure Toolbars... > Change Icon...

This button is grayed-out (inactive) for all toolbar items.

How do I change a toolbar item's icon?

Edit: Tested with both krita and krita-testing packages on Ubuntu 13.10

Weird, that does seem to work here on OpenSUSE, with a home-built Krita. It's deep-down KDE functionality, so I've no idea what the problem could be.

This issue appears to be present in the Windows version as well.

Can anyone confirm that the toolbar icons cannot be edited using Windows and Ubuntu Krita builds?

I can confirm this bug on a linux arch based distro. I'm using Krita Version 2.9 Pre-Alpha (git b493f1a) KDE Development Platform 4.11.4
I don't have the whole Calligra suite, only Krita.

Can someone try to reproduce the issue in another KDE application, as well as on a system with a full KDE Workspace installation? Please note that you will need to move the item out of the toolbar before you will be able to change it's icon (although once completed, you can move it back).

Okular has the same issue (add new item to "current actions", "change icons" button stays grey). By "full KDE Workspace installation" do you mean to install the full KDE desktop?

I can edit icons here ; Version 2.8 Beta 1 (git 91fd119) on Manjaro Linux Gnome-Shell ( I have a full KDE desktop installed on the same system too ).
KDE Platform Version 4.12.0

I've further tested this issue with all programs in the Calligra Suite for Ubuntu 13.10 64-bit version -- Kexi being the one exception since it doesn't appear to have a toolbar -- and was unable to change the toolbar icons in any of those programs.

Additionally, I noticed that selecting an item from the "Available actions:" list or "Current actions:" list within the "Configure Toolbars" window outputs the following error to the terminal:

QSpiAccessible::accessibleEvent not handled: "8008" obj: QObject(0x0) " invalid interface!"

Perhaps, this is relevant?

Edit: This bug seems to be unrelated. https://bugs.launchpad.net/ubuntu/+source/qtiplot/+bug/997462. Removing the package "qt-at-spit" silenced the error, but the icon issue still persists.

According to this thread, I was able to resolve the issue: http://forum.kde.org/viewtopic.php?f=17&t=89414

Solution:
Install kdialog (found in the kdebase-bin package for Ubuntu)

I hope that this information enables the maintainers of the Windows version of Krita to fix the issue.

tunacake wrote:Solution:
Install kdialog (found in the kdebase-bin package for Ubuntu)

Worked for me too. Thought I installed only kdialog, since it was available as standalone package (kdebase-kdialog for arch based distros).

Interesting. This indicates that a runtime dependency exists between the shortcuts system in kdelibs and kde-baseapps - something which shouldn't really exist (all runtime needs of the libraries are supposed to be shipped in the libraries themselves or in kde-runtime).