Thanks for the response! I appreciate your input.
I need to defer for financial reasons, not because I wish to work on the MA. And I was only accepted at the end of June and my financial situation has just changed in the last couple of days. I do feel bad about how late in the season this is, but, it was unavoidable. I'm not deferring for the MA program, the MA is just something I'm doing to cheer myself up while I wait to start law school next fall. Even if I didn't do the MA, I still wouldn't be able to attend law school this fall.
But, I understand the gist of what you're saying. I should not mention the MA at all, especially since it's inconsequential.
If something drastically changed and you cant afford it, just tell them that. If you happen to do some other classes while waiting for school to start, that shouldn't be a problem. You can always tell them about it later.