How do you get the popcorn to stay crunchy or not get hard from getting mixed in the batter?

I don't :P. Cookies just need to sit somewhere for a day or two and as they get drier, they regain some of the crunch. I was inspired by method of preparation behind pierniki that should be left to 'age' for a month or two to get the proper taste. It's a bit quirky, but many of our sweets seem to have been invented by sadists who want to strain your patience ;).

Regarding the 'candied lemon', I'm actually going to talk to with my mother and grandmother about that, because it would seem that it's a derivative of one of many recipes that were made during the period of food-rationing and general post-Soviet (thanks, Russia) lack of resources. It's sweet and chewy, but it's not just a rind. It's almost like a hardened chewing gum in texture. I'll share the method once I'll get to it, but you could probably use any type of candied fruit, since it's likely a long process done to cope with lack of ingredients :/. In the meantime, if you happen to have some Polish foods store near your area you could ask them if they know what I'm talking about.

As a side-note: since lemons, oranges, bananas etc back then were pretty much a luxurious good I think the method was initially applied to apples. Probably only around 1990 when that period ceased and borders started to open anyone used the method for other fruits.