Shell Programming and Scripting

I need a hint for moving around one file.
My aim is to put my script in the directory init.d to switch one file while booting the machine. It is about switching the resolv.conf before the networkmanager gets started. My script has got the 777 rights, but there is no such result as I intended to. So I want to move the real file to /tmp, where it will be removed after the next boot and replace it with another version of that file, with the same name but another content. Is it due to unix-rights for the directories, that this doesn't work properly?
The idea behind is, that before messing around with resolvconf-program and resolv.conf file, I just want to switch it on starting my machine, for having another list of DNS-addresses. And by the way, I am not sure where to place it in init.d to set it right before the network-manager starts.

So here comes my source code, not set to /etc yet, may someone has got an idea, thanks in advance.
Reading manpage of cp and mv did not result in inspiration.
To not destroy my init.d or network-connection
I am using the directories Desktop and downies.

Code:

#!/bin/bash 
set -e
set -u

# read exact path for usage
# PATH=$PATH:/$HOME/$USER/Desktop
# $0 the name of the script $$ is PID
echo "PID" $$ " and name of the script is" ${0};

V31=$(date +%X);

# spreaded writing with ""
ritmo4 ()
    { 
      echo "It's just been $V31"
      exit 0
    }

ritmo4;

# the file bla.txt has not an identical content.
# Version in /Desktop is different to the version in /downies.

mv -f /home/$USER/Desktop/bla.txt  /tmp | sleep 1s 

cp /home/$USER/downies/bla.txt /home/$USER/Desktop 

exit 0;

I'm not sure what your long term goal here is. If you are trying to run a script to change your DNS in /etc/resolv.conf this seems like an overkill. When not just make a backup copy of /etc/resolv.conf and directory write and make changes to that file to that file? Examples: What does "sudo echo nameserver 8.8.8.8 > /etc/resolv.conf" do? - Ask Ubuntu

After reading this linked page about injecting a DNS as sudo it became clearer to me, what you meant. But as I discarded sudo and just operate with su I found my mistake, that is in the function

Code:

ritmo4 ()
    { 
      echo "It's just been $V31"
      
    }

ritmo4;

Without this line it works properly. To explain my aim:
It is about to make a short list of TIER2 DNS in that new resolv.conf with lets say two functions included. To ping and tcptraceroute that server, wether it is up or not. After reading about dhcp and network manager, reading themselves, knowing that there is truly one special script that resets all my modifications, I decided to make that overkill on booting the system. So there remains just the question where to set the script b e f o r e the network manager starts to run. While booting it says "setting kernel configurations....done" then comes "configuring networkmanager...done". So in between there it should be.
And btw does anybody knows which script in debian resets all my modifications? I once tried to modify resolv.conf and on my old squeeze there are still two files of it, both named resolv.conf, but I can't figure out which one is doing the job. Thats why I would like to make that true radical overkill. And now bash cannot find the new bla.txt on the desktop, though it is there.