S Herman wrote:
So a non-IR pilot can file IFR, but cannot then execute that flight
plan, even if VFR conditions exist at all points of the flight?

That's correct. You have to be IFR rated to accept an IFR clearance
(i.e. to act as PIC under IFR). On the other hand, anybody can file
an IFR flight plan. You don't need to be PIC to be a data-entry
clerk.

How do IR students practice approaches, etc. when they don't have the
CFII aboard? With a safety pilot?

If the safety pilot is capable and willing to be be PIC under IFR,
they could do that. But, the answer you were probably looking for is
that you can just ask for a "practice" approach:

"New York Approach, Archer 25629 requests practice ILS 16 into White
Plains".

"Archer 25629, fly heading 180 to intercept the localizer, maintain
3000 until established, cleared ILS 16, maintain VFR at all times".