There isn't a definitive way to do it but what I do is:

I download as much raw footage as I could, then in my editor broke down each video into separate clips. I downloaded a number of ambient sounds videos of cities, parks, street sounds etc
Depending on what clips I want to audio swap, I open the clip in the save file with the sound I need. match up the real sound to my clips until I think it sounds right. I generally layer sounds too i.e. use 2 - 5 real sounds clips to make one skate 3 clip. If need be I sometimes leave the original sound on, but lower it volume by 60%. Add in ambient sound If I need to and then render the clip.

It sounds long winded, but once you know what you are doing and you remember which sounds are in which file etc I can audioswap a clip in about 2mins.

Enjoy.