I like the 'Merge' option when importing identity safe data.
Except that at the moment it defaults to the 'Replace Existing Data' option.
But I think it should 'Default' to the 'Merge' option.
Then if you miss or forget this selection choice, you can have a second go to 'Replace'.
At present, if you miss the option, it will 'Replace' it and you've lost all your current data for good.