Mxsmanic wrote:
I can't find any guidelines on the type of fixes or waypoints to be
included in the routing description of an IFR flight plan. I presume
you can use things like VORs and (?) airports, as well as airways and
anything indicated on IFR charts or procedures. But can you also use
VPxxx waypoints or other VFR fixes?

You can clearly use anything that defines an airway (but not T-airways),
and ground-based navaids like VORs and NDBs, unless specifically tagged
as "VFR Use Only". You specifically may not use VPxxx waypoints.

The reason for asking is that I'm wondering if a VFR flight plan with
detailed routing that lists specific waypoints and fixes can be easily
converted to IFR without changing the routing, should weather or other
factors mandate a switch to IFR for the flight.

You can google for a long-ago thread that describes how to file a VFR
flight plan that actually goes to ATC. If ATC doesn't have your flight
plan, you're starting from scratch when you want to convert from VFR to IFR.

Basically you check the "IFR" box on the flight plan form, then in the
altitude box you write "VFR045" for 4500 feet (or something like that).
Someone will correct me.

If you don't check the IFR box, ATC never sees your flight plan, just FSS.

Another advantage of this technique is that when you call up the next
facility for VFR advisories, they already know who you are and where you
are going. When the initial controller "departs" you, it initiates
sending a strip to each of the facilities down the line based on your
filed airspeed, just like for an IFR flight.

There was a lot of discussion about whether it is legal to check the IFR
box on the flight plan form if you don't hold an instrument rating.
Clearly the answer is yes, it is legal [dons flameproof suit].