I copied timer.svgz from /usr/share/plasma/desktoptheme/oxygen/widgets/ to /usr/share/plasma/desktoptheme/default/widgets/
to make it visible on dark theme. I use AlphaBlack Control widget to color panel.

Can you tell what to do to make it not be overwritten when Plasma update comes? Should I copy something to:
/home/user/.local/share/plasma/desktoptheme/
But what? Entire "default" folder from /usr/share/plasma/desktoptheme/
?