yes, this should be possibile.
As you probably know, webratio always needs the user-group-module entities and their relationship, but you are allowed to extend them with your specific fields. Thus, if you want to use your own tables, in my opinion you should follow these stesp:
- check whether your tables completely extend the user-group-module structure, or not; carefully check every attribute, the relationships, and the user_group and groups_module tables (N:N relationships); if something is missing, add it in your database using names at your choice;
- in webratio, remove the mapping from these entities and relationship;
- refresh the database icon, so that webratio is aware of your database tables;
- redefine the mapping, for both entities and relationships: for each entity, attribute and relationship, choose the corresponding name in your database;
- perform a synchronize, and import in the datamodel as new attributes every specific column in your tables not already loaded in webratio; eventually you may even rename these attributes.
At the end, you should have no errors in find model problems, and nothing to synchronize, at least for which concerns the user-group-module area.
Please ask detailed instruction if needed.