Well I feel like a fool! I've just finished my model of the TDI Kriss Super-V and just started my UV unwrapping in preparation for skinning. Keep in mind, I'm still but an amateur although not a complete newbie at this. However, I am human and, as such, made a big mistake and realized it all too late.

In the course of unwrapping my model I found that I had forgotten to connect two vertices, leaving an extremely awkward polygon which is obstructing my unwrapping process. (Image here) If I attempt to switch back to Edit Polygon mode from the Modifier List, it gives me a warning and then, after I have completed the manipulations and try to return to the UV Unwrap modifier, the UVs are completely destroyed! Is there no way I can just simply connect this edge without ruining the UVs? This would be incredibly demoralizing to do all this work only to have to re-do it for some simple mistake.

no,
since uv is all bout mapping 3d points onto 2d plane.
So even if you only connect to vertices and thus change order and count of vertices, sides and polygones, you loose the UV.
I am really sry for you.

Yes i think there's a simple way, you just need to collapse the modifier stack.
Right click on the list of modifiers, select Collapse All
(You probably need to collapse just "Unwrap UVW", but i am not sure. )
This will apply uvw to your mesh permanently. After that you can edit your model as usual and when you ready just apply Unwrap UVW modifier again, your uvw should look the way you left it.


EDIT: wow this post is old.. Feb 12, that's today, but what year , oh well