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In the 2014 Mac Mini, Apple does not consider any internal part of it user replaceable. Because of this, the warranty is voided if it is opened.
 
if you need to use a torx screwdriver or similar then I think you are doing something that apple did not intend. at best you may be offered warranty service on a discretionary basis.
 
I think this falls into the "you can do it but if you screw up it's your problem" category.

To be safe, just keep the original HDD and put it back in before going to Apple store for warranty service. Unless you damage something, there is not way to tell that you opened it.
 
Hope not. One mini started with an OEM HDD, then went to SSD + OEM HDD and now has two OEM HDDs. The other mini started with an OEM HDD then an SSD was added and the OEM HDD was donated to the other mini.

I could be in trouble if either mini ever broke. Naturally of course both have Apple Care on them.
 
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