Answers to this question state that one may lie / alter the truth for the sake of Shalom.
Can your friend assist you in your lie?
Let's say a close friend accidentally injured you, and you have a huge bruise on your arm. Your wife would be angry at your friend for injuring you, and it would upset her and you for some time. You don't want to make a huge deal about it, as it was an accident.
You tell your wife, instead, that you accidentally bumped into something that gave you the bruise.
- If your wife encounters your friend and asks him/her how you got the bruise, can your friend lie to your wife (on his own doing)? In this case he is helping to preserve YOUR Shalom Bayit.
- Is it halachically OK to ask your friend to coordinate with your lie, by requesting that he concur with the story you told your wife?
The above is a sample scenario. I'm asking about a general case of doing this when it applies to any situation of Shalom Bayit.