Leandro Heck

The related issue here https://github.com/FreeCAD/FreeCAD/issues/20776#issuecomment-2993799518 has been fixed. However, this one has not been resolved yet. Something else has broken the color of the mirrored object when using Asm4, but...

https://github.com/FreeCAD/FreeCAD/issues/22170#comment-composer-heading

Good, it looks like this is possible now.

I was thinking this way from the user perspective (which it looks like it aligns with your suggestion 2) Select 2 lines (same as when applying an angle), and then...

A quick and nasty implementation could be to add a name to the 3rd parameter (angle) if it does not have it already, and then create the new angle constraint...