If by common practice in development you refer to "feature toggling", then you might misunderstood its purpose. You make features via toggles, but eventually (after feature is tested and stable) you remove switches, so code won't become too complex, smelly and unsupportable (even in big projects with big teams).
But if your plan is to keep toggle forever as a part of the game arcitecture, it will cost a lot of time, not only during development of this change, but also after, if they decided to add new stuff (it would impact DLCs, bugfixes, mods, etc). I wouldn't choose this approach to support slightly different art style for the whole game. Way too much work for small returns