I know I’m a bit late in the game, but for what it’s worth, here’s another method I discovered using Blender’s standard mesh tools. (This assumes that you’re working in Edit Mode on a single mesh.)
Set your cursor to the target vertex, and switch to 3D Cursor pivot mode.
Create a line between the source vertex and the target vertex, turn on the length display in the “N” panel, and remember the value (or jot it down if you have a memory like mine).
Select the line and one adjacent line on the “child” mesh, select “Normal” in the Transform Orientation panel, and click the “+” to create a new orientation (it will be called “Face” in the drop-down list).
Select all the child vertices/lines in the child mesh, but do NOT select the target vertex.
Transform the child vertices by the negative value of the connecting length, in this case “G , YY, -1.803”.
Note: I would turn off vertex merging before doing this. In my example, typing “1.8” before the “03” may merge the connecting vertices, which would distort the transform relative to the other vertices. You can always eliminate doubles after the transform.
As far as applying this to multiple meshes, you could save a little time by applying this script in the python console, changing the value as appropriate:
bpy.ops.transform.translate(value=(0, -1.803, 0), constraint_axis=(False, True, False), constraint_orientation=‘Face’, mirror=False, proportional=‘DISABLED’, proportional_edit_falloff=‘SMOOTH’, proportional_size=1)
That way the vertex merging risk is eliminated. Of course, the ideal way would be to calculate the distance between the vertices and transform by the x,y,z vector, which would eliminate the need for connecting lines and transform orientations. But my python skills aren’t quite at that level (yet). A “relative transform” add-on would be awesome!