Some possibility. If your computer has two USB positions. Buy a second USB drive. Format as EXT4. Copy existing /home contents to this drive. Using old pendrive, from Knoppix 7.4.2 DVD create a new Knoppix system with say 12GB Knoppix system, remainder of USB as overlay (e.g. 16GB USB would give 12GB system and 4Gb overlay) Then start Knoppix 7.4.2, add your set up as you want, then mount second USB drive and use it to store documents etc as a separate USB drive. Thus documents etc are stored independently of knoppix version on system drive.