How can I install elementary tweaks on elementary OS 0.4 Loki Beta?
You can install redesigned version elementary tweaks on Loki.
sudo apt install software-properties-common --no-install-recommends
sudo add-apt-repository ppa:philip.scott/elementary-tweaks
sudo apt update
sudo apt install elementary-tweaks
Note: please, read elementary team's stance before installation tweaks.
I don't use any ppa. I manually downloaded the "elementary tweaks" packages from https://launchpad.net/~philip.scott/+archive/ubuntu/elementary-tweaks and I installed them with Eddy https://appcenter.elementary.io/com.github.donadigo.eddy.desktop