When the software to be installed is contained in compressed files called Tomes (the icon is a generic file icon with a tightly cinched belt around its middle), the program TomeViewer allows opening of the Tomes and direct expanding and copying of one or many files to a target volume or folder. Resource files are rather trickier.

Macintosh Installers may (there is no hard-and-fast case, which depends on the age of the System) give you the option to a) make a Clean Install, by relegating the existing System to a folder called Previous System Folder and installing a new System Folder; B) reinstall a new copy of a System over an existing installation of the same System version; c) upgrade or update (they are different) a System with a newer supported System version or update, or d) make a Custom Install, in which the user chooses the elements to be installed. (Caveat factor, or proceed at your own risk.)

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