I wonder if we have had any members that have recently moved into homes where LED lighting was installed everywhere at the time they moved in and replaced LED fixtures with fixtures designed for traditional lamps or undid any LED-converted vintage fixtures and converted them back to their original light sources. For example, has anyone converted an LED-converted fluorescent tube fixture back to fluorescent before or replaced an integrated LED fixture with an incandescent fixture and used incandescent lamps in it?

I changed the LED bulbs from 2700k to 3000K in a few of the fixtures but otherwise left them LED.  I need to save as much money as I can right now. 

I wouldn't call replacing LED with proper lighting downgrading, more the opposite 

I am asking if anyone has done the opposite of LED conversions such as replacing CFL lamps with incandescent lamps or LED lamps with incandescent lamps or convert LEDized fluorescent tube fixtures back to fluorescent for purely nostalgic reasons?

Technically only lighting enthusiasts would do this, for your average Joe, there would be no point unless they would choose GLS tungsten lamps knowing they provided heat and light to help take the chill off a house in winter?
With fluorescent, again, only lighting enthusiasts would be able to tell if that existing fluorescent batten still contains its original gear or not ready for a nostalgic re-fit.

As a lighting enthusiast however, I’ve never done that, I’ve gone from LED to CFL, but never back any further.

I've done some reverse retrofits before on fixtures I've obtained. I did a T8 electronic to T12 magnetic conversion on some fluorescent fixtures, mostly original T12 fixtures that were field retrofitted to T8 in service that I converted back to T12 after I obtained them.

In terms of LED to incandescent, I only rarely to do that, usually only for traffic signals as I prefer the old glass lenses and incandescent lamps in older signals. I briefly had some LED filament bulbs in some of my signals but I found incandescents to look more authentic.

I also reballasted a few HPS cobraheads for MV in the past but I stopped doing that now I have more "factory" MV fixtures and the stock HPS stuff is getting collectible now that LED is around.

There are some fluorescent fixtures I have that have gotten refitted for LED for the time just to save on energy costs, mostly the frequently used fixtures. I did make a exception for one frequently used fixture which looks a lot better with T12. Now I didn't hack them up for LED or even clip any ballast leads, instead using new wire and new sockets in order to avoid doing so. To convert back to fluorescent I just have to reinstall the original hardware into the light. My rule with retrofitting my lights has always been to not do anything irreversible such as clipping ballast leads, drilling into fixtures, or worst hacking up ballast covers etc.

Granted most people probably don't care about what kind of light source they have as long as it's bright enough and the right colour so most people outside the lighting enthusiast community probably don't bother. Besides with things like integrated LED recessed lights, it's quite a lot of work to change them with a incandescent compatible recessed can.

Even if I actually do something like that, if the lights work and don't bother me, I'd just run them until they die. Why change them if they work and I don't mind them?

Stuff is expensive nowadays. I'd probably retrofit lights back to their original light source with a few lights, but not all of them to save money. If the LED stuff is integrated stuff, yeah, I'll definitely change it to something that has replaceable lamps.

I've replaced CFL with incandescent before.