To modify a diesel engine for use with 100% biodiesel normally there are two modifications that are needed. First an improved filter system needs to be installed, the second is a pre-heater is used to heat the fuel when ambient temps are below around 30 degrees F The bio fuel has a lower viscosity and needs to be heated to flow through the fuel system.
Neither of these mods should preclude the use of regular dino diesel.
Mr Diesel originally designed his engine to run on peanut oil. They can be easily be modified to run on all kinds of fuel. Algae bio diesel holds great promise.
I have run my 7.3 on about 20% bio fuel in warmer weather months. It tends to clean the engine so it is important to carry a spare fuel filter. Burned fuel smells better. The performance is good because of the removal of dirt, but the fuel has slightly less power, not noticeable at 20 %.