Can I temporarily turn this off?

Add the Electric Grid Enforcer shortcut to your shortcut bar, or bind a key to it in Settings -> Controls.

The functionality is enabled or disabled per "force" (team) - building ownership is by team, so this is the best way to handle it. Enabling or disabling this by keybind or shortcut bar will affect your whole team.

This didn't affect my existing save?

Electric Grid Enforcer only changes cable connections when new poles are placed.

This isn't doing anything?

Place the Electric Grid Enforcer shortcut onto your shortcut bar, and toggle it to ensure it is enabled.