I'm new to vertex's
Does vertex hacking edit the texture's (polygon's) shape, size, or visibility, and how do I do so with Brawl Box?
Just letting you know, textures and polygons are completely different terms.
Vertex hacking is the same as polygon hacking; it changes the shape, the uncolored framework for what the texture is applied to.
Textures (sometimes called skins) have nothing to do with the shape. They are simply the coloring draped around the polygon. The way that polygons (models) determine where each part of the texture is applied, is determined by UV maps (don't ask me what that stands for). UV editing, a more recently popularized method in Brawl hacking, can make symmetrical characters asymmetrical, squish and stretch textures across polygons for better resolutions when designing textures, and etc.
Brawlbox is the backbone for opening up the files of Brawl. Vertexes and textures can only be edited by exporting them; there are no ways to adjust them inside Brawlbox (BB). However, animations MUST be done in BB.