Can one ask Swiss ATC directly for such a temporary VFR cancellation, or is it something they can only offer you?
Peter wrote:
Can one ask Swiss ATC directly for such a temporary VFR cancellation, or is it something they can only offer you?
Swiss ATC tend to be quite friendly and accommodating, and you should have no hesitation about asking them for anything you consider to be reasonable. If you ask for something they can’t legally do, or can’t accommodate for some other reason, they’ll let you know without any hard feelings. And they tend to be pretty proactive with suggestions, especially with routing when the weather goes south (read thunderstorms). Radar coverage and MVA is the key to maintaining IFR status.
Swiss ATC/FIS won’t bin a flight plan as is done in the UK. Once you enter Swiss airspace with an active flight plan, it will remain active with them until you close it or leave Swiss airspace. That’s always your call, not theirs. IFR/VFR is just a status of that flight plan. Sure, they need to reactivate IFR but they activate and terminate IFR all the time because there are so many Y/Z flights in Switzerland. If you terminate IFR in controlled airspace, then they’ll keep you on the frequency with a clearance and only release you when you leave it. In your case, you likely were with ATC (not FIS) all the time so a status change was pretty easy for them. (Re)joining IFR usually means you get a clearance in(to) controlled airspace with a “remain VMC” and an expected waypoint for change to IFR or at some later point in time an “IFR starts now”.
I use a IFR / VFR / IFR Yankee flight plan to fly Genova / Paris if the weather is nice over the alps.
Here is what I file :
LIMJ LAGEN L50 TOP VFR SPR IFR A1 DJL A6 BALMU R11 KUTAN LFPN
When i get to TOP (Torino) I cancel IFR and continue VFR, and when I get on the other side of the alps I call Geneva and pick up the ifr clearance to Toussus.
Very convenient
That’s going to be highly relevant for this 
But presumably you should carry a current Swiss VFR chart (or run one on a tablet) to make sure you don’t bust any P etc areas during the VFR section?
For example can you just go buzzing around any mountain just because Swiss have you on radar? Can they offer a general clearance to do that?
Yes, you should definitely have a VFR chart available if you expect to have a VFR leg. There aren’t any P areas, but lots of R areas that amount to the same thing when active. There is a DABS chart that gives the active areas for “today” and “tomorrow” here. In your case, besides active R zones you need to be aware of C/D airspace around all the military and civil airports.
If you take a look at the ICAO chart, you’ll see that there is a NE/SW line separating the northern “flatlands” (Mittelland-Jura) and the mountains (Alpen). North of the line, class C airspace floor is FL100. South of the line, class C airspace floor is FL130 with MIL ON (military active) and FL150 with MIL OFF. Both ATC and FIS are able to provide information about activity of that, R zones, and all the military CTR/TMAs. Getting a crossing clearance is almost never a problem in my experience.
Be aware that “buzzing around mountains” is a popular activity with VFR pilots in good weather, especially around the Matterhorn and Eiger/Monch/Jungfrau, both in the 13000-15000 ft range. 
Peter wrote:
OTOH Swiss cleared me “DCT HR” and perhaps they knew that would be ok w.r.t. “R” zones?
Why would Swiss ATC not be able to clear you through any Swiss airspace, including restricted airspace, regardless of VFR versus IFR? Is there Class A airspace on the route taken? Why wouldn’t en route ATC coordinate with any local C and D airspace control?
Peter wrote:
OTOH Swiss cleared me “DCT HR” and perhaps they knew that would be ok w.r.t. “R” zones?
Certainly. If (still) flying on a clearance, then you’re fine. Sounds like you stayed with ATC and kept your squawk (rather than being transferred to INFO (124.700/126.350), so you were still being controlled. You’d be in controlled airspace the whole time anyway (even it was E at some point). In Switzerland you always know when you’re being released by ATC because you get “radar service terminated, squawk 7000, cleared to leave the frequency”. If your initial contact was on an IFR flight plan, then you’ll still be flying on the last clearance until you hear those magic words, even if IFR is terminated. IFR termination alone doesn’t cancel a clearance.
Silvaire wrote:
Why wouldn’t en route ATC coordinate with any local C and D airspace control?
In this situation (VFR leg between IFR segments), I would expect them to do so. Normally, on a VFR plan one is transferred to the airspace owner frequency to get crossing clearance. It sounds here like @Peter was talking to the same controller the whole time on a clearance (DCT HR) so there is no concern about R zones. If one decides to do a little “buzzing around mountains” that isn’t really covered by “DCT HR” so an amended clearance would be needed.
VFR in France, when flying through complex airspace with multiple owners/frequencies, it varies. Sometimes the first agency will negotiate crossing of an intermediate military CTR, especially if one will be coming back to them later. But I’ve also had a frequency change to contact a military zone owner for crossing.
@chflyer: To be honest, I fly only VFR, but I disagree on Swiss ATC being always so accommodating. FIC tries to avoid you from airspace Charlie as if it would be a prohibited area, even if you ask for a clearance. However, if I contact the DELTA frequency instead of INFO, they always try to arrange something and especially general class C crossings will get approved quite quickly, as long as the military doesn’t fly in the specific area. I guess, the INFO-operator has enough workload and doesn’t want to spend his/her time with coordination with Radar/Approach controllers. Even if I hear an aircraft checking in on a Z-flightplan with Zurich Info, FIC seems to be overstraind by the situation. Meanwhile, the Delta-Frequency is always very quiet, most foreign pilots don’t know this frequency. Interesting detail: The colleague operating INFO is located direct next to the DELTA operator, so they should keep in contact with each other. But I never heard an INFO-operator saying “for clearance, contact Delta” to any aircraft on the FIC-frequency. They just say “airspace C crossing not possible”.
This however, doesn’t mean that I dislike Swiss ATC at all. On the contrary, I like Swiss ATC for its professionallism and the “less is more” attitude in phraseology. Obtaining a class D CTR or TMA crossing is always very easy, even crossing Zurich CTR isn’t a big deal. Only Alpnach cancelled my clearance twice after obtaining one and gave me some strange instructions to some very small villages or mountain passes and handed me over to Meiringen or Buochs.
