I could be good to have a safe add_node function, which will do the same as add_node, but it the position is not loaded, save the change and do it after the map block is loaded.
Well usually when you hit an 'ignore' one of two things will happen: the block will wrongly replace a surrounding block, or if you have a later/earlier version with the fix in builtin/item.lua, the block won't place at all until the area is loaded.
I am mainly thinking to mapgen mods, for example landup, which will sometimes want to modify a node in a unloaded/ungenerated area, ignoring what is there, but for now it will not work.