Regarding the tweaks you mention, since this are the objects listed on p.7 we see no indication of the fishhook beig a weapon of any kind (others like the pickaxe are listed so). Also, we interpret that any object mentioned at the rulebook takes a slot (top line of p.8 says so) whether it's mouse made or human made, being the only exception to this rule the two slot objects such as two-handed weapons, armour and objects listed as large like the human made padlock and key.
Feel free to add a damage rating to the fishhook if you think it can be used as a weapon. Also, if you consider that the mouse made objects do not take up any slot, just do not use their cards.
As the game says at p.20, feel free to create and adapt rulings and make the game your own!