I am not so sure its a bad idea to give the home owner a copy of his woking file, if he/she only wants to make minor changes.
If you explain all of the pitfalls, possibility of corrupting the file, making a change that is wrong and he then can't figure out what to do next, making a change that changes other programming, etc., and the home owner still wants to do this, the only harm is his/her calling you back to get paid to fix it.
We do have a few clients that think its fun to do, and do it well. We do have a couple that keep us busy correcting their changes.
It brings good will and some new project referrals.