Importing doesn't transcode anything so you're not going to lose quality on an import. But exporting can be many things. If you're exporting from a timeline then it matters what codec. Yes, even if it's the same settings. Codecs like h264 (which you shouldn't be using anyway) are always going to re-compress.
But if you're working with ProRes or DV or DVCPro for example, then exporting with "current settings" and "make self contained" will make a COPY of the in/out area of your sequence to export. If the clip didn't need to be rendered in the sequence, then there is absolutely no change in the data from import to export. If you reimport that file again, it of course retains it's quality because importing doesn't do anything to quality.