Doing this way (NG_DESIGNER), will the administrator have to gives privileges on any new object instance (variable, folder, interface) of the project ?
or is it possible to restrict the privileges on specific project, but giving every privileges on the sub-objects of these project (without giving them one after another) ?
By the way, what is the difference between NG_DESIGNER, and NG_REPOSITORY ?
No the administartor just gives access to the objects and their actions that sit under a project. You do not have to do it on an instance by instance basis, although this granularity of object security is also possible. Take a look at the following odiExperts article which gives a good overview of the security setup I'm referring to
Its for 10g but still holds true for 11 & 12
To answer your last question the DESIGNER profile is used for people who need to develop ODI processes i.e. create, modify objects in the repository. The REPOSITORY EXPLORER profile only allows a user read-only (view) access to the repository objects.