No, you don't need to render again.
Why do you need to render the video in the first place? Is it because of some effect or because of the format and codec the video uses?
To speed up the render process you might consider a faster storage medium though, as many flash memory drives have low read and write speeds like 10MB/s or so. A dedicated FW HDD will give you better results, but that may be too much if you only have one or four GB of video data. Even storing the video on the internal HDD would speed things up, even though it is not recommended to use the HDD with the OS stored onto to use as scratch drive for media files.
Also make sure the sequence settings and the video and audio media files match in as many aspects as possible, foremost the codec, framerate and resolution. That will reduce render times and even the necessity to render at all.