Is there a way to specify the center of rotation in Sketch? Normally it simply rotates the object around its center. If there is no native way maybe it's possible to write a plugin!?
As spiral said, the functionality was added in version 3.2. To use it, you will need to select the layer you want to rotate and either click the Rotate tool in the toolbar or select
Layers > Transform > Rotate Layer.
Once you are in Rotate mode, you will see a small target that you can reposition to change the center of rotation.
This functionality was added in Sketch 3.2