Justatest, keep in mind that everything in SL is, at its most basic level. an asset. All "in-world building tools" do is allow one to change the parameters/attributes/properties of an asset after you rez (instantiate) it.
Moving a single vertex of a mesh, however, would require a new asset to be created, since vertex placement is not an attribute or parameter but is intrinsic to the asset itself- embedded as it is in its collada file definition (as is a pixel color in a texture).
Of course, you could script prims to represent vertices, edges and faces and have a way to interact with them to arrive at some configuration that would then generate a collada file somewhere that could then be uploaded to the asset server, much as the in-world sculpty makers do to generate sculpt maps. However, it wouldn't be trivial.