In the Dexpot main program folder (usually 'C:\Program Files (x86)\Dexpot'), create a subfolder icons. Again, add a folder called e.g. newicons. Put your custom tray icons there.
Create a string called "TrayiconSet" in 'HKEY_CURRENT_USER\Software\Dexpot' and assign the name of the folder containing your icons (in this example "newicons") as the value.
Dexpot Portable: Open the portable.ini in the Dexpot main program folder, add the line "TrayiconSet=newicons" to section [Dexpot] and save the file.
Restart Dexpot afterwards.
Icons for Desktop 1-20:
d1.ico to d20.ico
Icons for the active Desktop 1-20:
d1a.ico to d20a.ico
Icon for the next desktop:
next.ico
Icon for the previous desktop:
prev.ico
Default program icon:
dexpot.ico
Icon for the tray container:
container.ico