Adding the magnifying glass and phillips requires you to add the whole layer, including the backspring. The one from the file will not work as it's too thin and doesn't have the right end parts.
Here's a How to for basic mods:
http://forum.multitool.or....msg181175.html#msg181175You can find it as a sticky at the top of this subforum too.
It explains how to take a SAK apart and put it back together again. You'll need pin stock to replace the original ones. Rotokid at edcsource used to have some but I think he doesn't have any at the moment. Try searching hobby shops and the like for the right size, 2.5mm for the outside pins and 2.2mm for the centre one. I know some people used welding rods too in a pinch.
Ask questions if you encounter any problems, we have a few good SAK modders here and they are a friendly bunch, always happy to help a new guy out.