@rajibando, I revived the old thread since I thought it was still relevant and useful. Sorry about that.

Please allow, to explain better what I am looking for.

1. I have knoppix on my usb to fix PCs and also do personal work.
2. I do not always use the same PC and/or laptops since clients vary and all have their hardware, wifi settings. printer configuration, network settings etc etc.
3. Sometimes I need to install software specific to a certain situation. Example I install a program that I need to use in one place and not in another. So it is useless having all the programs I need in one overlay file.
4. Therefore it would be nice if I could have a knoppix-data.img on every user's hard drive partition with settings, data and software specific to the user/machine. Then once I boot knoppix from my usb, knoppix would ideally search all the partitions looking for the img file and if found, it is used as the overlay file.
5. Like this, I would not need to have 4 or 5 overlay files on my usb and then rename them according to the environment I am working in.

Hope I was clear in my explanation... How can this be achieved please?

Thanks for your time.