is a specific kind of: replace, supersede, supervene upon, supplant.

is a broader term that covers: cover.

derivation: subbing, substituting | deputy, lieutenant | deputy, deputy sheriff | deputy, surrogate | backup, backup man, fill-in, relief, reliever, stand-in, substitute | reserve, second-stringer, substitute.

is a specific kind of: appoint, charge.

derivation: delegating, delegation, deputation, relegating, relegation | deputy, lieutenant | deputy, deputy sheriff | deputy, surrogate.