sg_change_nodes_p(
  proxy,
  data,
  value,
  attribute,
  rate = c("once", "iteration"),
  refresh = TRUE
)

sg_change_edges_p(
  proxy,
  data,
  value,
  attribute,
  rate = c("once", "iteration"),
  refresh = TRUE
)

library(shiny)

nodes <- sg_make_nodes()
nodes$new_color <- "red"
edges <- sg_make_edges(nodes)

ui <- fluidPage(
  actionButton("start", "Change color"), 
  sigmajsOutput("sg")
) 

server <- function(input, output){

  output$sg <- renderSigmajs({
    sigmajs() %>%
      sg_nodes(nodes, id, size, color) %>%
      sg_edges(edges, id, source, target)
  })

  observeEvent(input$start, {
    sigmajsProxy("sg") %>% # use sigmajsProxy!
      sg_change_nodes_p(nodes, new_color, "color")
  })

}

 if(interactive()) shinyApp(ui, server) # run