It looks like I am able to reproduce this issue when I am editing the preset using the preset manager. If I go to Insert->WebAssist->CSS Sculptor and make the changes using that interface, I can save the preset with another name. It will generate a page when you save the preset, but it is a workaround that would allow you to save the preset you generated under a different name.
Another workaround would be to duplicate the design before editing it, that way you'd have the original and the duplicated preset.
I will log a bug for this issue. Please use the workarounds to get around this issue.