Can you sync an iPhone to a different comp if you sign into their account?

Can you delete, the download something, then back up the phone on a different computer if you sign into their apple account, and then sign out afterwards?
i know this is confusing, but i want to jailbreak my friends phone, and hes willing to type in the password to log into his account on my computer. On another question, it says this basically, but does not mention if their signing into their friends account on the computer, or not.
Please hurry!
and Thank you for anyone who answers!

Yes but it would delete your account/personal information on the iPhone and sync whatever data is on your friends computer. If you were to sign out then sign back on with your original account and try to sync it on your friends computer, it would delete it again. Account has to be the same on the phone and computer to sync back and forth and use apps. For example, apps stored on your account that you purchased, won't work under your friends account.

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