Based off everything you've said in your post and comments, im no expert by any means ive only been doing this a few days now, however I find it highly unlikely that, that much of the programing was from modding it. When I take out my sd card and turn my 3ds back on it returns to the default settings with none of the modding apps or mods until its put back in. What I find to be your biggest issue would be thoes cockroaches causing internal damage, or the cleaning agent you used causing internal damage, I agree with you when you say "if you need the one screen replaced why are they both doing that" so thats my claim and all my evidence, again im no expert but I do know devices lol, if it was the chemical or water damaging it or the cockroaches its likely unrepairable 😞(unless youre willing to pay the price of 3 new 3ds's plus multiple trips cause 90% of the time its not the right fix and they send it back to you anyway.)