Is it possible to rotate a part of the sketch in the editor?

Yes, it is. Click one of the rotate tool icons on the left side. You can choose to rotate both clockwise and counterclockwise. When the tool has been selected, you will see a 0 appear directly under the lower left corner of the sketch area. This is the number of degrees to rotate the objects.

Use the right mousebutton to change the value. Right-click to increase the value, hold one of the shift key on the keyboard and right-click to decrease the value.

When the correct degree of rotation has been set, left click on the object you want to rotate. The position you the curson has when you click will be the point the object will rotate around.