Hi Xristos,
no, you absolutely can't add user roles in a SQLite db.
SQLite is a _PERSONAL_ DBMS intended to support just a
single user, and consequently supporting user roles is
a complete nonsense in such an environment.
Hint:
I suggest you to start by reading first the SQLite's own
documentation so to get at least a generic familiarity
with the basic SQL engine before adventuring yourself
in more complex tasks involving the SpatiaLite extension.
and a quick glance at the Cookbook will surely help you
to understand and master SpatiaLite in a very short time.
[1]
https://www.sqlite.org/lang.html
[2]
http://www.gaia-gis.it/gaia-sins/spatialite-cookbook/index.html
bye Sandro