Why don't you also apply the changes on-the-fly? (Sorry if you did already, I haven't tested it yet).

EDIT: It's OK in creating the tuning script, doesn't change the parameters on-the-fly.
You could separate the two functions with two buttons in the bottom of the screen, one to "apply settings" and the other to "make settings permanent" - or you could have one button only to make the two things. I prefer the two buttons solution.
Also, if you want, don't forget to add /proc/sys/vm/vfs_cache_pressure which is another interesting parameter to play with.

Finally, I propose that you change your package name to swappolube-gui so that we can have the plain swappolube to change the parameters to a given profile for those who don't want to tinker with tuning, and the swappolube-gui package for the adventurous ones who want to make their own config.