you need to make sure the item is of the same type, i have not tried using "force" much.
as an example to change copper to steel:
changeitem m INORGANIC:STEEL
i quite often use it with autodumping if i'm in a cheating mood (i.e making decent rooms for dwarves quickly, stack up a bunch of beds/tables)
so dump designate a huge bunch of metal bars/anything
autodump here
puts them all on the same location
changeitem m INORGANIC:STEEL here
changes all items in the stack into steel (platinum can be cool too)
changeitem q 5 here
changes all items in the stack to masterful
be hugely warned, this is some cases is going to send MASSIVE migrant waves and MASSIVE goblin sieges at you, especially if changing to adamantine.
I lost shortly after the 12 million dorf bucks greaves (well, i held off the siege but half my fort was dead and too lazy to try and resurrect it).
The migrant wave immediately after making it was 34 dwarves, which just about doubled my population at the time.
you can change single items but you need them selected by name on the left (i.e, to select a made bed use "t" to select buildings parts then change it), to select a single item use k to view, -/+ to select if in a long list. Can also select items dwarves are wearing,
I do not think you can change the decorations item type. So if you want to try it on a mood, use v to view the dwarf as he picks up each item from the stockpile for his mood, and edit.
Can also use "t" to select his workshop, not sure if it works after it's said he's begun making his masterpiece (thinking about it, i can't see any reason why not)