Can you mod the hunting rifle on fallout new Vegas

Yes, you can find the mod parts in various locations, and they can generally be found in trader's sales inventories for a reasonable price. There are three mods for it that I know of, which should be all of them as I believe no gun has more than three mods for it. These mods are a Scope, to allow for easier long-range sniping; a Custom action-bolt, to allow for faster firing; and an extended mag to increase clip size. However, if you have a unique Hunting Rifle (a Hunting Rifle with a special name, usually accompanied by a change in aesthetics, value and stats) then you won't be able to mod it as unique weapons aren't customisable.