EDIT: Okay, let’s start over, I don’t think I explained clearly what I’m trying to do.
This is Aiko3, she is a fully rigged character model for DAZ or Poser. I want to create a morph for her, that is, changing the shape of her face or body slightly; this can be done by sending her out as an .obj, editing that .obj in another program (ie: Blender) and then bringing in a new .obj with the same vert-order but a slightly different shape. Currently, Aiko3 is perfectly symmetrical; I want to keep her that way while I edit her so that the morph I create is also symmetrical. If I was working on something original, I’d just use the mirror-modifier, however, in order to create a morph for DAZ, I have to keep the vert-order the same as the original, so I can not cut Aiko3 down the center and use the mirror modifier on her. Instead, I wanted to know if Blender has a function where it would be able to pair up identical vertices on the two sides of the X-axis and be able to set those to mirror each other, so that I can work symmetrically without creating any new vertices or deleting any existing ones? The most important thing here is that I must keep the vert-order the same as when I imported the .obj.
OP: I have a human figure, I’ve altered one side of the mesh slightly and I want to mirror the effects of what I did over to the other side, but I don’t want to cut her in half and use the mirror modifier because I’m trying to make a custom morph of one of the D/S millennium figures, so in order for that to work, I can’t change the vertex order or anything, just push them around. The base figure I’m working on (Aiko 3) is symmetrical, I’m trying to alter her chest size, is there something I can turn on before I start pushing the vertices around that will make it effect both sides at the same time, or is there something I can click afterwards that will make what I’ve done to one side pop over to the other?