[THEME] Sony Concept ROM navigation bar icons theming

I thought theming the Sony Concept ROM wasn't possible, aside from using icon packs.

But I found an APK that allows to change the navigation bar icons.
Does anyone know how this is done? (Or is this a theme meant for non-Concept ROM (Sony stock ROM) that somehow also works for Concept ROM?)
Also, are there more APKs that do Concept ROM nav bar theming?

APK: http://ift.tt/1Y1cKoC
Source: see comments at http://ift.tt/1Y1cmXd

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