Okay, here's my take, based on a quick review of
the 18F452/8 programming spec...Note that I
have never made a programmer, so I don't know
for sure if this would work, but here is my
evidence...

I don't think the LVP pin state is of any consequence.
The flowchart for HVP says nothing about it, but
it does state that upon 'MCLR/Vpp = Vpp, all inputs
become high impedence.

Furthermore, at the end of the document, a Vdd
setup time is specified as 100 ns before Vpp rise.
However, and this is important, NO MAXIMUM time is
specified.  To me, that means that, regardless of the
state of the processor when 'MCLR/Vpp goes to the
programming voltage, the PIC enters a known state
from which it can be programmed.

This does not take any errata into account, or any
experience with unannounced "features", such as
Olin's 18F1320 discovery, but at least by the book,
the PGM state is unimportant.

Mike H.

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