You can try doing some changes,but it is not recommended and changing the settings in the global settings tab will end up worsening your experience i.e. it will apply changes to all games even the ones that doesn't need any while simultaneously you can suffer performance hit.
Something that you should change is the v-sync option in manage 3d settings and set it to adaptive.This way you'll always get smooth frame rates but not higher than 60 fps.
However nvidia has preferred to use high quality texture filtering specifically for the game skyrim(not to be set through global settings).
Games do come out with poor anti-aliasing techniques.So for these games you may use FXAA On and disable the in-game anti-aliasing mode.Again do not set it in global settings,select the game you wish to tweak for from Program settings and then apply your changes.
Yes you can... by keeping aa mode to enhance application setting.
If you have enabled a setting like anti-aliasing from control panel then use only that setting otherwise both the control panel aa setting and the in game aa setting will be applied and that might end up being to much for the gpu to handle.Same goes for other settings such as anisotropic filtering,ambient occlusion,etc.