If you type "flags." into the console (ctrl+shift+i) it should pop up a list of all the currently active flags that you can scroll through. It's not an ideal solution since if you haven't encountered a flag yet it won't show up (like "ratputation" doesn't show up in the list until you actually meet the rats and the flag is first set) but at least you can use it to find and change flags you've already encountered. And if there's too many flags to sort through, the names are pretty straightforward so if you're looking for, say, ratputation you could just type "flags.r" and shorten the list to all the flags beginning with the letter r.