I normally (and I am) running a 52/36 with an 11-28, which is perfect round here where a 1.5miles climb is a rarity. Actually its was fine for 5 months of lock down cycling back home in Fife (but probably nothing over 3-5miles of continuous climb 3% ave with the occasional 10-21% spikes at the extreme). I’m looking at booking a weeks winter holiday to some where warmer like Tenerife which has me thinking about my gearing. My chain is pretty new (less 400 miles) and the Fifer in me 
feels it would be a shame to shorten it for a week. I think I’ve got a 34t 4 bolt ring in my cupboard somewhere. If I was to swap out the current 36 to a 34 for one week would I see any significant problem with chain drop or shifting? Or is there something else I should consider?
I did that for a trip to the mountains in NC. Biggest issue was chain slack in the small / small gearing combo. But as long as I kept the chain on the 14t or above when in 34t ring, it was fine.
It’ll be fine. I typically run Shimano 52/34. The shifting could be smoother but I haven’t had a problem with slack and dropped the chain just as frequently as with a regular set up
I ran it for a good six months. I did drop the chain occasionally, enough that I added a chain catcher, but it’s entirely possibly I didn’t quite have it dialed in. And shifting from 34 to 52 was a little worse. I’d happily run it again if I had to for a trip or something, but I do prefer the shifting of “properly” matched Shimano chainrings.
I run 52/34 with 11/32 in the back, I only ever have issues with chain slack when I get down to the 4th from smallest cog in the back. You’ll be fine as long as you are mindful of where your chain is 
While front shifting may suffer a bit from mismatched rings (especially under load), on rides featuring very long climbs where you may only front shift a handful of times for the entire ride, this may be quite acceptable. But in terrain featuring lots of short rolling climbs, this may be more of an issue.