Is it possible to switch from VFR to IFR and back?

Ron Garret writes:

Just ask ATC for a clearance. If they aren't too busy they will just
give you one. If they are busy you will need to contact flight service
by radio to file an IFR flight plan, then get back in touch with ATC to
activate it.

Do I have to work out a whole list of waypoints and stuff to give to
them? Can I just ask for IFR clearance to my destination (or to some
specific point where I expect to find VMC again), without specifying
waypoints or altitudes?

Usually I have a VFR flight plan which in fact does include waypoints,
because I've worked something out with a chart beforehand, but not
always. If I've filed a VFR flight plan that mentions way points, can
I refer to it when asking ATC for IFR clearance? In other words, just
convert part of the VFR flight plan to an IFR flight plan?

Landing somewhere first is also an option.

Yes, but if I can't see anything out the window, this is not without
risk (mainly from conflicting traffic, even if I have instruments that
allow me to land in poor visibility).

Yes, you can switch from IFR to VFR at any time by simply telling ATC
that you are "canceling IFR."

Do I get in trouble if I file VFR, encounter IMC, and have to ask for
IFR clearance as a result? I know I'm not supposed to take off in
IMC, but it seems like on a trip of substantial length, it's hard to
guarantee that it will all be fair weather, especially in some regions
of the world (the area around Seattle seems very pretty, although it
also seems that one can rarely _see_ the area around Seattle).

Why? People fly IFR in VFR conditions all the time.

I recall reading that the vast majority of private pilots (80%?) are
not instrument rated, and that many accidents involving small planes
occur when non-IR pilots fly into IMC and become disoriented. So I
assume that it's rare for the pilot of a small plane to fly IFR
"unofficially" while under VFR. It sounds like a lot of them have no
idea how to do it.

It's much better to be IFR the whole way if there's any chance of
encountering instrument conditions anywhere on the flight.

Because ... ?

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