Re-installing software/apps from a backup

I am contemplating fitting a new hard drive and was wandering after a fresh install of OSX would it be possible to copy a particular app from a back up i have onto my MBP. I have a couple of old apps to which I have lost the software/serial number(activation codes). So can it be possible to just connect my back up disk and drag the app over?

Any help/tips will be much appreciated.

Generally applications are better if a fresh install is done but give it a try. If it works well ands good, if not it has cost you nothing. You should be able to access the codes from the software manufacturer.