Hello Harmesh,
Its quite simple. Now that you have upgraded your new SRX to the version you wanted and have copied the display set file on it, you can follow the steps below :-
1. Remove all the existing configuration.
root> edit
warning: uncommitted changes will be discarded on exit
Entering configuration mode
[edit]
root# delete
This will delete the entire configuration
Delete everything under this level? [yes,no] (no)yes
2. Now load the new configuration.
root# load set /var/tmp/<CONFIG-FILENAME>
root# commit and-quit
root>
This should resolve the issue.
Note that when you add new configuration, some parts like interfaces simply add to existing configuration instead of overwritting it. This is because sections like interfaces may cater multiple families and IPs.
Hope this will help you.
Thanks!