You don’t have to wait for the battle to be over. you can change either of those things at any time on your turn. the deck changes just don’t propagate until it’s reshuffled. The equipment does, though.
Also see above re: the hourglass. Lets you spend AP to “scout ahead” (not sure what that does as I haven’t used it), spend a ration to camp and regain 10 HP/AP, spend AP to “prepare” one of four class cards, or escape the area (in adventure mode at least) and go back to the menu where you can go to town, etc.
PSA: Nether Horrors are fuckers. Perma-flying, so you can’t damage them except with ranged and indirect damage. Immune to Kill, Weaken, Vulnerable, and Sneak Attack, so that’s Shadows out. Plus Bewitched, Burning, Envenomed, Immobilized, and Entangled. And huge resistances to Piercing (most ranged weapons), Poison, Dark…everything except Fire and Slashing, basically. You know, all those ranged Slashing attacks. Only weak to Consecrate, Blessed, and Banish. Demon Shadows have neither of the former, and the only reason I had Banish is I recruited a unique priest ally with a multicast undead blasting spell and a Circle of Protection that’s mostly defensive but can do a whole 6 points of Banish…which does nothing unless they’re down to 6 HP. I basically only managed to kill it because I had a few Alchemist Fire Bombs and sometimes I could find them in my backpack, combined with occasionally managing to hit a Double Damage roll on my throwing knives so they did anything at all. Oh, and they’ll randomly sneak attack you in the middle of doing stuff on your turn, not sure if there’s a specific trigger. I wasn’t in any serious danger, I had ally generated 19 HP worth of healing every turn and a ton of concealment and echoing defense, etc, and I obliterated reinforcements instantly. But what a slog.