Best practice would be to create a new inventory item and then do an inventory adjustment out of the old item and into the new one at the same quantity and COGS, then inactivate the old item. That way you’ll easily see the transaction that gets created and there’s much less potential for messing something up.  This SA article also seems to say that changing accounts is not advisable Account Information on Items (see that Important note/box).  As to what exactly is going to happen that depends on exactly what account you’re referring to, what your item settings are, what your accounting preferences are, whether you have any customizations touching this item, and potentially some others things I haven’t thought of.  Honestly you’d just have to give a go in sandbox, see what happens, and test very thoroughly if you’re dead-set on going that route.