General :: Unable To Setup PATH Using Shell Script?

I am creating one bash script name as pathsetup.sh.

In that , I am trying to setup a path to my user profile. S my script content is as follows,

pathsetup.sh contains,
#!/bin/bash
MY_PATH=/home/arun/NS3/ns-3.9/build
export PATH=$PATH:$MY_PATH
echo "$PATH"

If I run the script, when run time it shows the MY_PATH added to PATH.

But, when I check it in terminal after run, it doesn't add the PATH.

if I put echo $PATH in terminal, it show old path.

How can I add path permanently to a user.

I read, ~.bash_profile , we can add the path permanently for a user.

But, I want to add MY_PATH for a specific time. I don't want any user change the file .bash_profile each time.

Just running the pathsetup.sh script, MY_PATH should be added to the user PATH.

Instead of .bash_profile, using shell script, can it possible to add path permenetly for a user.