What Is the Proper Way To Make Changes To Mesh That Will Be Reflected in UV Map?

When I switch to edit mode and make a mouth the opening doesn’t show in textured paint mode. How do I get that to happen please? Do I have to start over(Make a new uv wrap) every time I want to make a change to my mesh?
See screenshots:


So far as I know, the answer is “basically, yes.” You really need to get your mesh just the way you want it first, before you move on to texture-painting or anything involving UV’s. (X,Y,Z) and (U,V[,W]) are two entirely separate coordinate systems.