By default, sketches that have been defined by sketch relations or dimensions won't be changed by any subsequent sketch relations and dimensions. However, there are two settings that can cause the sketches to behave differently. As an example, a fully defined 50mm x 50mm square sketched using the rectangle tool will be used in the following sections.
Detach Segment on Drag
Enabling this option (located in Tools->Sketch Tools->Detach Segment on Drag) will cause sketch segments to not stay attached to any other sketches that it borders. Dragging the right line segment will cause it to detach.
Override Dims on Drag/Move
Enabling this option (located in Tools->Override Dims on Drag/Move) will cause the dimensions to be both driving and driven. Dragging the right line segment will drive the horizontal dimension and cause it to change.