Unfortunately, I found that even with a Sim who had nearly maxed his handiness skill, any farming upgrade parts I cheated my sim (by shift clicking on an animal sheed or coop) did not register in my sim's inventory when I tried to do a particular upgrade. You know how certain upgrades require 6 parts or whatever. The game would only count the upgrade parts my sim had obtained through the errands with Kim the grocery lady. (I found this out because I had five parts and tried to cheat myself one more, but the game refused to count it). I also found it wouldn't count farming upgrade parts that I had another sim gift him with for some reason. It's all very odd and probably has something to do with the errand system.