How to add vertex/edge labels to existing graph

Question

If I have already created a graph using Graph. Later, I want to add to the graph some vertex and/or edge labels, how can I do that?

Thank you.

Answer 1

A random graph without any labeling:

g = RandomGraph[{11, 21}]

You can use SetProperty to add labeling P.S.

SetProperty[g, {EdgeLabels -> {3 \[UndirectedEdge] 4 -> "COOL"}, 
  VertexLabels -> {1 -> "STUFF"}}]