[BiMMate]

FYI, I inherit my own class from MultiLineNode and added Wash and Paint methods that make the trick:

private readonly LineMaterial originalMaterial;
private static readonly PropertyInfo? MaterialProperty = typeof(LineBaseNode).GetProperty(nameof(DimensionLineMeshNode.Material), BindingFlags.Public | BindingFlags.Instance);

public void Paint(LineMaterial mat) => DimensionLineMeshNode.MaterialProperty?.SetValue(this, mat);
public void Wash() => DimensionLineMeshNode.MaterialProperty?.SetValue(this, this.originalMaterial);

public DimensionLineMeshNode(string name, Vector3[] positions, LineMaterial sharedMaterial)
    : base(name)
{
    this.originalMaterial = sharedMaterial;
    this.IsHitTestVisible = true;
    this.Material = sharedMaterial;
    this.Positions = positions;
}