I am not an ODI developer, but am suddenly responsible for an ODI instance. We have a new source database (ORACLE), identical in structure to the old, but with a new name. My question is, is it possible to modify a physical schema once it has been established? Can I 'repoint' to the new database without modifying every package and scenario?
Yes, you may modfify the physical schema without any need to modify your code. ODI works with the Logical/Physical/Context concepts, so your code is pointing to a logical schema only (not to a real DB). This logical schema then points to a physical schema when used in a specific context. With this kind of Logical/Physical/Context concepts, ODI allows you to modify any physical detail without change to the code itself.
By the way, congrats on the new gift (your ODI instance)