I can't make any statements regarding retrofits, but I'd be happy to share my experience with a new construction and some photos that may shed some light.
First I'll share what I know. The steps on my pool (18x36 IG Vinyl Grecian) simply replaced the entire wall panel at the center of the shallow end. The steps are fitted between the two 'corner' wall panels and sit on the footing with tublar pillars.
The steps have a gasket that the liner covers, and there is a bracket that screws over the liner during installation (like around your skimmer opening) and a finishing strip to cover the screws. This is attached during the liner installation, and excess liner cut out after the initial fill but before getting up to step level.
I guess the difficulty for you is going to be determined by how hard it is to remove concrete decking, skill of your builder (or yourself if a DIY project), and the ability to find steps that will fit based on where you want them placed.
My builder swore by the Quaker brand plastic steps, and I've been pleased with their build quality. I also had hydro jets installed and plumbed in during the build (about $80 extra) but that might be difficult in a retrofit build.
Here are the photos of my pool construction from start to finish. There are some detail shots of the steps: http://www.andyandersons.com/index.p...view_album.php
There are lots of shots with good detail on how the steps are installed, as well as how the liner was installed over them duirng and after the initial fill.