[graph-tool] Adding a subgraph into a graph

Hi, I have one query about modifications with graphs. There is a subgraph that I identify using pattern matching and remove it. The intention is to replace that part with another graph. Using the graph_union function the graphs are combined structurally, however, all the properties of the graph being inserted are lost. Is there any way for insertion of subgraphs with the properties preserved? -- Thanks, Kavya