How can you save an app's data?

Question

Hi, how can you save an app's data? For example, if I want to switch some applications on my iPod with those were on my iTunes Apps Library, iTunes will force to remove the apps that was on my device and sync the apps that I want onto my iPod. But once the app is removed from my iPod, its data will be erased too, so, for example months later, I want to put them back onto my iPod, I will lose all the apps data and games progress. So, I just want to know the way that people save their apps data.

Answer 1

Yo can't. apps are locked to the account thatpurchased them and in-app purchases can only be mad with the account that originally purchased the app.
You will have to recover use of the first account
How do I change or recover a forgotten Apple ID Password?
If you've forgotten your Apple ID Password or want to change it, go to My Apple ID and follow the instructions. SeeChanging your Apple ID password if you'd like more information.
If necessary:
Forgotten Security Questions/Answers
You need to contact Apple by:
1 - Use the Express lane and start here:
https://expresslane.apple.com
then click More Products and Services>Apple ID>Other Apple ID Topics>Forgotten Apple ID security questions.
or
Apple - Support -form iTunes Store - Contact Us
2 - Call Apple in your country by getting the number from here:
http://support.apple.com/kb/HE57
or           
Apple ID: Contacting Apple for help with Apple ID account security
3 - Use your rescue email address if you set one up
Rescue email address and how to reset Apple ID security questions
For general  information see:
Apple ID: All about Apple ID security questions
If you have not uses any of the $10 you redeemed to the new account, you can likely get that refunded by contacting iTunes
Contact iTunes