The index doesn't contain objects themselves, every added file (whether it is committed or not) is held as a regular object. The index simply holds a list of o

The index doesn't contain objects themselves, every added file (whether it is committed or not) is held as a regular object. The index simply holds a list of object ID's. So yes, if you change a file and re-add it, the index will be overwritten and the original object will become dangling without any references to it.