Hello Francesco,
As I understood, the "snipped" is like any other SMath file, but if you save it in the "snippet" folder you can insert into your existing worksheet via Snippet Manager (as collapsed area or not). Therefore, just make the *.sm file and pay attention on File=>Properties. There are two options "Summary" and "File atributes". What you put in the Summary - Title that will show as a snippet title ( I suppose that you did not put anything there and that is way the snippet description is the same as your file name - with *.sm added). What you put in the File attributes - Snippet shortcut - that name will appear in the Dynamic Assystance (in order to insert in via Dynamic Assistance, if you lke).
I hope this is the answer to your question.
Regards,
Radovan
When Sisyphus climbed to the top of a hill, they said: "Wrong boulder!"