Supplant means to “take the place of.” Supplement means to “add something to complete a thing.” For almost any grant you write, it is important for you to begin a new program or to supplement a program rather than to supplant one. While most grantors make that fact very plain in their grant literature, some are not as explicit. Regardless of that, you can rest assured they do not want you using their money to supplant a program you already have in place.
Most grantors are interested in helping you to improve academic performance in some way. You can usually do that by implementing a new program that has shown promise in other schools or by expanding a program that has been successful in your own school. You usually have to come up with the money for that new or expanded program. Grantors often supply that money.