The pilot in the left seat has his PPL, no instrument rating, and is
practicing flying under the hood. His buddy is in the right seat, PPL
+ instrument rating.

The left seat pilot is the sole manipulator of the controls, so he
logs PIC. The safety pilot in the right seat was designated as PIC
before the flight, therefore, as acting PIC, he logs PIC.

They fly into IMC. The guy in the left seat is still controlling the
airplane, so he still gets to log PIC. Now, since the flight has gone
into IMC, there's no longer a safety pilot requirement. So the guy in
the right seat no longer gets to log PIC, since his presence is now
superflous.

Who's ACTING PIC now? The guy who's logging PIC in the left seat does
not have an instrument rating so he can't ACT as PIC...but he's the
one at the controls. Does the guy in the guy in right seat retain the
ACTING PIC title, even though he can't log that PIC time?

Alex