If it has the same name then the original version isn't overwritten by 'import'.
BUT you can 'Reload' it simply by selecting a placed instance [or it's icon in the model tab of the Component Browser] and select that right-click menu item; if it's not the the same folder as it was originally you'll have to navigate to it... A 'Reload' will then update all instances of the originally imported component with the current version in the external SKP file...