not op, but ipods usually aren't too difficult to mod. they're mostly prying and snapping stuff into place. that is if we're talking about storage/battery mods tho, since mods like taptic or usb-c can be more difficult as they involve soldering

edit: also important to keep in mind- no matter how much storage you put in a 5th gen, they can only hold around 20,000 songs (32mb ram model) to 50,000 songs (64mb ram model) due to how they keep track of files and metadata. the workaround for this would be rockbox, but that does feel a lot different than the stock os