WordNet sense 1 (filling again by supplying what has been used up):

renewal, replenishment, refilling

WordNet sense 2 (someone who takes the place of another person):

alternate, surrogate, alternate

WordNet sense 3 (a person who follows next in order):

successor

WordNet sense 4 (an event in which one thing is substituted for another):

permutation, substitution, switch, transposition

WordNet sense 5 (a person or thing that takes or can take the place of another):

substitute

WordNet sense 6 (the act of furnishing an equivalent person or thing in the place of another):

replacing