Mesh:setVertexAttribute
Sets the properties of a specific attribute within a vertex in the Mesh.

Meshes without a custom vertex format specified in love.graphics.newMesh have position as their first attribute, texture coordinates as their second attribute, and color as their third attribute.
Mesh:setVertexAttribute( vertexindex, attributeindex, value1, value2, ... )
vertexindex number The index of the the vertex to be modified (one-based).
attributeindex number The index of the attribute within the vertex to be modified (one-based).
value1 number The new value for the first component of the attribute.
value2 number The new value for the second component of the attribute.
... number Any additional vertex attribute components.