I have a solution:
Get "Resource Hacker" and start it.
Open the file "LiberKeyMenu.exe" in "%LiberkeyRoot%\LiberKeyTools\LiberKeyMenu" with Recource Hacker.
On the left side you will see something like a folder list.
Select "Icon Group" then "AAA" then "1033".
On the right side you will see 6 LiberKey Icons.
Rightclick on "1033" and select "Replace Recource".
Click on "Open file with new icon..." and select an other icon.
Save the file. This will create a copy of the Original Liberkey file and a new one with changed icons.
That's it.