Consolidating is a one-time process that makes a new copy of any track that is outside of the designated media folder inside the media folder and reconnects the iTunes database to that new copy. iTunes ignores the original thereafter. If you attempt to add it again iTunes will do so, since it doesn't match (by filepath) anything already in the library. You only need to consolidate media if you add it to iTunes when it is stored on paths outside of the designated media folder, and you have the option to "Copy files to iTunes Media folder when adding to library" turned off. Anything ripped, purchased, converted or transferred from a device already ends up inside the media folder.
Changing the media folder tells iTunes where to store newly added content in future. iTunes will also ask if you want to consolidate the existing content to the newly selected media folder. You should not need to change the media folder as part of any backup process, unless we're talking about making a split library portable to simplify things in future. Again if you do this then you're looking at a one time change that you won't need to revisit. Changing the media folder path is not the way to switch between libraries, that is achieved by holding down shift (Windows) or alt/option (macOS) as you launch iTunes and then choosing a different .itl file. The advice on making a library portable can be applied equally well to data that is on internal drives as external ones.
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