I'm creating a script to change the icon theme, color scheme, font size, etc, and I get it. but do not know how to update the settings without needing to restart or logout session from commandline. I know it is through Qbus, but I have no idea how to do.

You will need to interface with KGlobalSettings and D-Bus in order to make this happen - as well as Qt itself, so creating a QApplication instance would be advisable.
Please see kdeui/kernel/kglobalsettings.cpp in kdelibs for more information on this process.

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