It's simple. It's best to do everything in a separate, external folder.
In "main" folder are *.svg files and important file: main.qrc
You can rename the main.qrc file with your own (ashjuk.qrc) to avoid confusion.
Important: It's best not to change ANYTHING inside the qrc file, because you don't need to.
Change your graphics while keeping the original svg file names.
After that, it is really enough to run the command rcc:
Code:
rcc.exe --binary ashjuk.qrc -o custom_icon_theme.rcc
Copy your custom_icon_theme.rcc file to the Sigil settings folder.
You can find it easily by going to "Preferences" and pressing the button in the lower left corner of this window.
The last thing is setting "Custom icons" in "Preferences".
Restart Sigil and enjoy your own icons.
If necessary, repeat the last steps (rcc, copying the result file to the settings folder, restart Sigil).