Need a specific feature to edit template

Recently I use template to build my local ebook library index which I use one of my book information as template and using this template in other book. This is really a fluent exprience.
But I found there is not any way to edit an existing template, and I even could not delete an existing template. They just exist, and only way to change them is change the original block which template refers to, this behavior will let specific templates disappear.

I think we may need a specific feature to let user edit existed template.
Make templates as some kind of config and store locally.

User can edit their template but pages already use template would not be changed, only template itself changed

Next time user use this template, the info become which user has changed.