This is not possible.
You should have only one project type with code ADM (administrative), one with TMP (template) all others are OPE (operationnal)

If you do so (for instance updating database) you will get unexpected behaviors

I understand thanks you babynus.
I've got one more question, i've got few projects and now i want to change their type from OPE to ADM but projeqtor is telling me "workflow doesn't allow you to change to this state"
is their any solution or do i need to delete all my projects and re import it with the right type?

No, it's just a misconfiguration of your workflows, set on project type.
It means the projects you try and change are in a status that does not exist on target workflow (defined on target type)
Just change your workflows