Retaining quality while re-encoding with same codec
It can depend on the compression used, but generally yes, there will be a loss of quality, particularly if there is any alteration to the video.  For a fairly low compression format like DV it probably isn't going to be much, but the best bet, if the format supports it, is to append the stream data and alter the file such that it has the necessary format or simply make a virtual clip if your editing environment supports it.

Personally, I've always taken the latter option when working with DV, so I don't recall if it is a format that easily supports combining files or not, though I would expect it is since it compresses every frame independently as I recall. (May be wrong on that though, haven't worked with DV in a while.)