Is there a way to disable certain questions?
I keep coming back after long breaks and the "practice" feature that is used to review old topics keeps giving me questions about the sounds hiragana characters make. The problem is I already know all that stuff and don't need to practice it, what I want to practice is all the other stuff that I'm starting to forget. Is there any way to avoid being flooded with these questions?
No, but you can try doing more of the tree. That forces the hiragana and other intro questions to compete with the newer lessons.
I realize this isn't a real solution to your question, but it works for me.
I'd've probably stopped doing this course by now if there wasn't, but... No, there isn't any way to disable them... ^^
However, it is possible to skip the character matching exercises whenever they appear. On this particular type of exercise it doesn't penalise you at all for clicking the skip button on them. In fact, Timed Practice even gives you 1 XP every time you skip them! :D
The character matching exercises are extremely tedious to do on a PC using a mouse. They're clearly designed with touchscreen devices in mind, as unlike every other exercise this type has no keyboard support. The other types of hiragana and katakana exercises aren't too bad since they take no time at all and can be answered effortlessly with the keyboard.
(Also, it is possible to disable "listening" exercises by disabling the "speaker" option on the "settings" page.)
I don't believe there is a way to disable them, however, you can go back and practice specific lessons. Once or twice a week I choose a lesson to review for the day just to reinforce what I learned.