I have removed the custom address for A Yorkshire Memoir and reverted to the original taskerdunham.blogspot.com (instead of taskerdunham.com). If reading this, you are in the right place.
This is to prevent the blog from becoming inaccessible when the subscription to the custom domain expires. It still has over a year to run, but I have made the change early because custom domains are often bought by others for illicit use.
Thanks.
Technical and Other Considerations (for anyone considering doing it themselves)
Removing the custom address turned out to be easier than anticipated. I thought I would be wrestling with the technicalities of canonical names (cnames) and the like, but that was not the case.
All I had to do was:
1) Delete the custom domain name in the blog settings. The blogspot.com version of the address worked straight away. The taskerdunham.com address began to be shown as unknown.
2) I created a completely new blog called "A Yorkshire Memoir (Old Address)" saying what I was doing, and also a note in the title that the address had changed.
3) Then, on the Old Address blog, I simply added www.taskerdunham.com as the custom domain. Surprisingly, that URL immediately began to redirect to the "Old Address" site. It did not require any change to the cnames on the domain provider's site. It did, however, take a few minutes before the https version of the address became active after I switched it on.
The outcome is that access to taskerdunham.blogspot.com now links straight to the active blog, and access to taskerdunham.com links to the "Old Address" site. I will leave it like that for now as a reminder to those who use that route to change their links.
Please let me know of any problems.
Internal links within the blog - The blog archive, list of popular posts, etc. changed automatically. Links in blog posts that reference other posts still work correctly so long as they point to a taskerdunham.blogspot.com address, but if they point to taskerdunham.com a message appears saying either that the post does not exist or that the site cannot be accessed at all. It depends on how http/https and www are specified in the link. Fortunately, I have always used the blogspot version within the blog, so don't have to change them.
External links - Where others' blog posts or websites have included a link to one of my blog posts, these links now point to the "Old Page" site, i.e. taskerdunham.com, with a page not found message. The same happens with sidebar links on other Blogger blogs until they are updated.
Google, Bing, and other search indexes - Initially, the results from searches remained unchanged, i.e. they referenced the custom address. Clicking these links led to the "Old Page" site, i.e. taskerdunham.com, with a page not found message. I assume the search indexes will automatically update in due course, but it may take several months.
I was soon receiving emails from Google to say that pages addressed as the custom domain could not be indexed, and they disappeared from Google search, but the .blogspot.com versions did not appear either. I have tried forcing the issue through the Google Search Console which appears under Crawlers and Indexing in the blog settings, but do not really understand what I am doing.
UPDATE October 2024: Google search has not caught up yet. Some of the previously most visited posts no longer appear. Bing and DuckDuckGo seem better. The hit rate has gone down to at best a third of what it was.