We organized an ISBN for a book last year, while it was still in the planning stage. As the book develops, it looks like the title we gave with the ISBN isn't quite right, and another title would be better. Is it too late?
In the US, the ISBN registrar Bowker allows changing the title. Their FAQ does not say anything about the ramifications of doing that.
If you got the ISBN from someone else, ask whoever assigned the ISBN to your book.
Once you assign an ISBN, your registrar will distribute the information, e.g. to Books In Print. So there my be catalogs with the old title, at least until the registrar distributes the update.