When creating a new line, you can 'Tab' select the angle and length options and also the angle between the first and second line in sequence. But the 'Dimension' tool doesn't work on lines to give us back these options.

If we could select a line and hit '=' to bring up the 'Dimension' tool then enter a length to resize from its center, or additionally select an end CV as an anchor and either length or angle value would be from that point.

Additionally if you selected two joined lines you could enter a value for the angle between. This may need my previous post 'Selectable lines/curves that are joined' in order to work.