Let said that I like Mr. X's and Mr. Y games and would like to bundle his games with mine. I had completed the bundle and now waiting for Mr.X approval. Mr. Y approved. However, Mr. X does not response for a very long time and I now don't want to do business with him. Now here is the trouble I ran into. It seem that once I get into the 'waiting for participants approval' stage I cannot remove nor delete games I had chosen. So what do I do if I want to swap out Mr. X's games with Mr. Z's games or just do me and Mr. Y's games.

You should abandon the bundle and create a new one if you wish to change the arrangement. We do this so someone doesn't join a bundle, then have the whole thing change under them.