How to add a shortcut to a task manager without reloading the shell for a shortcut to appear?

Development
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As I’ve found, it is stored in ~/.config/plasma-org.kde.plasma.desktop-appletsrc, under [Containments][147][Applets][150][Configuration][General]. I’ve found a way to edit it with kreadconfig6 and kwriteconfig6, but to apply changes (a new shortcut to appear), I need to reload shell, which is not ideal in my case.

I took a look at Kickoff launcher’s source code. I found a reference to this model, but this is just a representation of data, as far as I understood.

By researching source code further, I’ve found that it’s probably this what does the job:

onLauncherListChanged: {
    Plasmoid.configuration.launchers = launcherList;
}

As far as I know, Plasmoid is a widget/applet, so I probably can’t access this myself from a standalone Kirigami C++ app. It isn’t that much of a problem, if I can edit manually with kreadconfig6/kwriteconfig6, but I need to somehow to tell the task manager to refresh the configuration (as I understood, when it modifies its own config, it happens automatically? I wasn’t able to find something responsible for refreshing in Kickoff source code), so that’s my final question.

Or, well, to avoid XY problem, I also ask for any other ways to programmatically add shortcuts/launchers to application launchers that don’t require to reload the Plasma shell for new shortcuts to appear.

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I use “Icons-Only Task Manager” to create a 48px wide Unity-style left sidebar with launchers for some frequently used apps, and manually add various “Actions” (apps and scripts under the same category as the main app) in their custom “.desktop” files under “~/.local/share/applications”, which are manually edited from time to time.
I then run the command kbuildsycoca6 in a terminal window to refresh the app launchers with their context menus in that “Icons-Only Task Manager”.
If I understood correctly, this command might be what you’re looking for…