How to render separate audio and video and after mix them for dvd

Good Morning All

I use kdenlive since...

I am working with image from camera and audio from professional recorder.

I can sync, + or -, but it is hard to render all the project if some mistake.

It is nice to have the video ready, rendered and after make small changes in audio and render separate.

Which formats to do so?

And how to mix them?

Many Thanks
Gaspar Santos