Currently I am now aware of any way to change the Global Theme from the CLI - either one would need to manually call kreadconfig5 and kwriteconfig5 to replicate what kcm_lookandfeel is doing, or use the GUI. It would be great if this module could support args, so that I could for example call kcmshell5 kcm_lookandfeel --args "Theme=Breeze" to change my Theme to "Breeze", without needing any human interaction. Something like this has been requested across multiple places, e.g.: https://forum.kde.org/viewtopic.php?t=123361 https://www.reddit.com/r/kde/comments/8oq8vm/change_kde_color_scheme_from_terminal/
Implemented by Dan Leinir Turthra Jensen with https://invent.kde.org/plasma/plasma-workspace/-/commit/2c2cd9babf2470bbb7ad1aa8626b1508204cfa24 in Plasma 5.22! See `plasma-apply-lookandfeel --help`