Sorry to double-post but I decided to test a structure and upgrade based on what you're looking for, it worked fine, but....
Adding the PrerequisiteOverride=NARADR tag will mean you won't be able to train anything that needs a prerequisite as NARADR because to YR, that building no longer exists once you over-write it.
But there
is a cheeky little way by cloning any and all units who require NARADR and give them [upgrade name] prerequisite, or of course re-building a NARADR.... (but in some cases where structures with build-limit of 1 can complicate anyone new to this).
I'm pretty sure I've got a working formula for something simliar to the Age of Mythology branching tech-tree (where you chose a God which upgrades certain units over others). In this simplified case choosing to upgrade either research buildings, i.e. war factory, barracks or defence building.
