With source code obviously yes, though it would need interfacing between Python and C++ (likely used in GTA V), then internal screen resizing, and as most of the time is spent in OpenCV anyway it might not give you the effect you wish to get.
I don't know much about c++ reverse engineering but I've done this when reversing iOS apps (and this is what "tweaking" means in the jailbreak community). The same concepts should apply.
The first step is obtaining a class dump (what it's called with iOS) that shows you all the header files and gives you the information necessary to understand what's going on in a debugger so you can determine which method to hook.
Edit: this should point you in the right direction - https://rafalcieslak.wordpress.com/2013/04/02/dynamic-linker...
(Just in general, doing this shouldn't depend on a particular game, it's a graphics API level thing)
http://www.geforce.com/whats-new/articles/ansel-revolutioniz...