Issue updating an Edge arrows at runtime ( making it bidirectional )

[Schuket]

Hi!
I'm using WPFGraphControl and trying to modify an edge with a singular target arrow to a bidirectionnal one, which would have both source and target Arrow.
I tried modifying its attribute (ArrowheadAtSource), but if this was at None or NonSpecified when the Graph was generated, it lacks some critical structure ( the arrow itself and the arrowPath ).
And modifying its attribute triggers ValueChanged -> Invalidate, which tries to access unexisting value.

Am I using the wrong flow to modify the arrow of an edge ? Is that not doable at runtime ?
Do I need to fully redo the graph for it to work ?