Partial Restore of Emails

I am trying to restore emails from a backup on cpanel for just one folder inside of a user's mailbox. I am a user of a major hosting provider and fairly inexperienced in using cpanel. There is a restore feature in cpanel but it wants to restore all the email and gives me a scary message saying that all email will be overwritten with the backup if I click the button. I've tried with the support from the company and they haven't been responding to me. So, I have two questions:

1. If I do the restore of the emails inside of cpanel, will it wipe out all of my mailboxes and replace them with the information from the backup I'm using? (Meaning I will lose all emails in the system since the backup) Or will it simply add in all the emails from the backup that aren't currently on the server?

2. I downloaded the complete cpanel backup in zip and tar formats to my local machine. I can see the emails that I need to restore in the folder in the compressed files. However, I'm having trouble extracting them and uploading them due to illegal characters in the file names. I had the understanding that I could just FTP the missing emails up to the appropriate folder under /mail/ and they would be restored. I'm unable to get them to upload though. I've tried on windows and linux. Is there another option to do this?

I would prefer to do the option in question one, however I have to get it done by tomorrow or the backup that I want to restore from will be overwritten on my hosting provider by another weekly backup and with the level of support I'm receiving from them I don't think I can get them to save/restore the backup for me.

I appreciate any help with this.