Man ... you must really think we are all idiots!!
No offense, but at least on my side, I am sure that I checked the enable button and then pressed apply , then changed the themes. It didn't work.
Then I added the UseTheme=true manually, and then tried to change the theme again using that same KDMThemeManager .. didn't work.
Then undoed all the changes , removed your package , installed the new one .. and it worked like a charm. Maybe it works for you ... it didn't for me ... and by what it seems like .. neither for a few more.