yocto do_install() cp overwrite?

Question

I want to implement my yocto project recipe bb file like this:

do_install() {

  install -d  ${D}/usr/www/ ${D}/etc 
  cp -R  ${S}/code ${D}/usr/www/xxx
  **if statment**
  cp -Rf  ${S}/customer/code ${D}/usr/www/xxx
  install -m 0644 ${S}/config/lighttpd.conf ${D}/etc/lighttpd_hitron.conf

}

if some statment is true, it will using cp to overwrite the usr/www/xxx 's code folder, but it seem not working, the usr/www/xxx 's content still the same,

and if do this it will work :

do_install() {

  install -d  ${D}/usr/www/ ${D}/etc     
  cp -R  ${S}/customer/code ${D}/usr/www/xxx
  install -m 0644 ${S}/config/lighttpd.conf ${D}/etc/lighttpd_hitron.conf

}

so i assume that its cp's overwrite fail? or some other reasons?

thanks all a lot！