Explanation

Total Return Swap (TRS) is the most appropriate instrument for changing commodity allocation because:

• Total Return Swap provides exposure to both price appreciation/depreciation and any income (such as dividends or interest) from the underlying asset
• It allows investors to gain synthetic exposure to commodities without physically owning them
• The swap receiver gets the total return of the commodity index, while paying a floating rate (typically LIBOR plus a spread)
• This is ideal for portfolio managers wanting to adjust their commodity exposure

Other options:

• Basis swap: Used to hedge basis risk between different but related commodities
• Excess return swap: Only provides exposure to price changes, not the total return

Therefore, B: a total return swap is most appropriate for changing commodity allocation.