I also like making differently sized decks and wish there was more support for doing so - but I understand why it's better to stick to a standard resolution. Luckily, you only need to save the deck as the new size once and then it will continue being that size each time you open it. That being said, I recently made a contraption that allows you to export decks at a different size, if that helps you at all.
Edit: When I initially wrote my reply, I missed the part about wanting to change the size of the deck without having to close or reopen it - sorry! Here's a script that will do exactly what you're trying to do, but again - you may find some issues to work around if you plan on doing this.
on newres x y do
# cut the 'deck.encoded' output into chunks
endeck:"\n\n" split deck.encoded
# get the first chunk, which is {deck}
d:"\n" split endeck[0]
# find the 'size:' tag and edit it, though it's usually on the fourth line.
each v k in d
if v like "size*" d[k]:"" fuse "size:[",("," fuse x,y),"]" end
end
# rebuild the deck from the chunks.
endeck[0]:"\n" fuse d
endeck:"\n\n" fuse endeck
# open the newly edited deck and refresh the page.
danger.open[newdeck[endeck]]
danger.js["window.dispatchEvent(new Event('resize'));"]
end
Using the danger interface differs between native and web Decker, you can read more about it here. For testing purposes, I exported the Decker Tour as .html and changed 'DANGEROUS=0" to 'DANGEROUS=1' From the Listener or through a widget script, you can trigger 'newres[200 200]' or something similar to see how it affects the window.