Shiny : How to modify reactive object

I have a reactive object that i want to modify when the user click on the GO button. I tried this code and Per gives a great result. Now I want to do more than one modification considering the first one, so It seems like I should save RA_s every time I modify it.

How can I handle with this problem ?

Code

shinyServer(function(input, output) {

  RA_s <- reactive({
    read.csv("C:/alay/Desktop/RA.csv")
  })

  Per <- reactive({
    if(input$go == 0) return(RA_s())
    else {
       c = RA_s()
       c[1] = rep(0,nrow(RA_s()))
    }
   c
  })

      })


sidebar <- dashboardSidebar(
  sidebarMenu(
    menuItem("Download", tabName = "d")
)
body<- dashboardBody(
  tabItems(
    tabItem(tabName = "d",
         actionButton("go",'GO!')     )
  )
dashboardPage(
dashboardHeader(title = "Valo"),
sidebar,
body
)