A codicil is a specific document designed to do a specific purpose, to amend a will It must be a stand-alone document. It must be written in ink. It must say that it’s a codicil. It must be witnessed by two parties and it must be signed by the person doing the codicil. There are other criteria is no point in going into them here. Even if that’s what you wanted to do, amend a will, the chances of the wording of the document in your book actually doing that is remote in the extreme which is why solicitors draft them specifically to suit individual circumstances.
I cannot think that what you’re doing even resembles a codicil. I think that you probably misunderstanding what a codicil is.
A letter of wishes is simply that. Basically it is a non-legally binding document which explains what people want to happen after their death. You could incorporate a letter of wishes into your book but I think the chances of a standard document doing what the person wants is unlikely.
I think what you are proposing is an excellent idea because it puts everything with regard to a deceased person’s affairs into one place and it would certainly make an executor and many solicitors jobs much easier after persons died if everyone had such a document or book.
However it’s of no legal effect but from what you’ve said, it doesn’t appear to need a legal effect because it’s more of an information document than anything.
With regard to any comments made even in a will with regard to cremation or burial or suchlike, this is not actually enforceable in any event so there’s no problem having it in your book.
Can I clarify anything for you?