I always use hotkey 2 for my pistols. I found a work around. Go to My Computer/documents/my games/FalloutNV and open up the FalloutPrefs.ini (back it up just in case). Find the [Controls] section. Under it, find the Hotkey entries. Here's what mine has (I changed the ammo swap to "Q" in game. Yours might be different.

Hotkey1=0002FFFF
Ammo Swap=0010FF01
Hotkey3=0004FFFF
Hotkey4=0005FFFF
Hotkey5=0006FFFF
Hotkey6=0007FFFF
Hotkey7=0008FFFF
Hotkey8=0009FFFF

Change it to

Hotkey1=0002FFFF
Ammo Swap=0010FF01
Hotkey3=0003FFFF
Hotkey4=0004FFFF
Hotkey5=0005FFFF
Hotkey6=0006FFFF
Hotkey7=0007FFFF
Hotkey8=0008FFFF

You will lose "8" as a hotkey (it will now be 7 on your keyboard) but at least you have 2 back! In the pipboy if you assign something to "2" it will still show as "3" in the little popup screen, but it still is assigned to "2." In theory you can assign the hotkeys to any key as long as you know the hex string for the letter or number on your keyboard. I hope this helps any frustrated people who keep hitting 2 like me to change to their pistol.