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I have a Panasonic Lumix DMC-GF7 which I use to shoot timelapse movies. Because of the electronic shutter, I figured it shouldn't cause problems, but I noticed a second issue: On every frame, the camera does its metering wide-open and then steps aperture back down to what I actually selected.
Will this ruin my lens in the long run? (It's a Lumix 20mm 1.7 if it makes a difference). More importantly, can I make the camera stop switching the aperture all the time?
Could be, but it is unlikely with a lens designed specifically for a camera system also targeted to semiprofessional videographers, which also seems to have a timelapse function built in. They would likely not include it if it caused extreme wear in a standard configuration - the last feature a manufacturer wants to include is one that prematurely breaks equipment without a way to blame it on the user (which they could if they made people use external intervalometers etc...). Doubly not on a budget priced camera where the cost of arguing with entitled customers will eat into their margin.
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About stopping that behaviour anyway:
This might or might not apply to the GF-7 specifically, but many DSLM designs will not meter wide open if you set them to any exposure mode that has a manually set aperture (M or A at the very least).
Alternatively, if you can get away without autofocus, use an adapted manual lens - the camera has no control over the aperture that way, which will stop it from operating it with absolute certainty.
Alternatively - but this COULD ACTUALLY CAUSE EQUIPMENT FAILURE or raise power consumption significantly, depending on camera/lens design: Check if there is a DOF preview feature assignable to a button, and tape that button down.
I'm not sure anyone can answer this definitively, but I would guess that the iris and its actuator are probably one of the longer-wearing parts of a lens like that. A common cause of failure is fatigue in ribbon cables that are flexed in some lens models during focus movement, so I would probably be more concerned if the lens was auto-focusing for each shot. In addition, the mass of the moving parts for the aperture is very small, which means there isn't much in the way of jolting impacts going on, and hopefully not an unsustainable amount of friction.
