Wow, I’ve found a workaround to simulate a feature I wanted in the past: edit symmetrycal meshes on both sides, because sometimes you wish to edit the mesh on the left, times on the right…like in ZBrush. You cant do this with a symmetry modifier for example.
You can do this by first mirroring the half-mesh as instance. Then you have two separated objects but they’re instances of each other, if you modify one you’ll modify the other, but you cant edit the two at the same time. If you want to work on the other side, you need to exit sub-selection level, select the other side and enter sub-selection level…no good, inpractical…but here comes the trick: select these two sides and go to menu Group>Group and create a group. Now when you select this group you have the Editable Poly at the Modify panel, and you can enter sub-selection level and start editing on both sides.
Then my idea was to add a Vertex Weld modifier with a very small weld value to weld the vertices at the center seam, but there’s a problem =(. As the 3dsmax’ documentations says, when you apply a modifier to a group, 3dsmax applies on instance of the modifier to each object in the group, then it wont weld the seam =( …I would like to apply the modifer to a kind of collapsed group…not sure if its actually possible. Then apply a TurboSmooth…
Well, hope this helps, and if you have a solution to that problem please share, I would be vary happy to see this thing working…I find this useful, gives us more freedom to edit the mesh…