If you express the no contact (via an email so there is no circular crazy making conversation) for yourself, then I think it is an appropriate thing for you to do. If it is something you need to do, for yourself, then it is a good idea. If it is something you need to do in order to follow through on it, then do it.
If you do it expecting him to honor that or whatever, it is pointless.
I do get wanting to share your intent once, for yourself. It is what I wanted too. I did something like that. I told him (in an email) that I would communicate about the kids but I was no longer talking about anything else. He did not respect that (of course!) nor did I expect him too. I said it once (and did follow through) for my own peace of mind and what I felt was the right thing for me to do.