Set major mode for all visited files by extension

[Tim Johnson]

Using GNU Emacs 26.3, X toolkit

With my configuration, when I open emacs and load a session, it appears 
that a modified auto-mode-alist entry is consulted *after* the 
associated major-mode from the previous session is used and is therefore 
ignored.

A practical application is if I have been using the built-in elisp mode 
for .el files and then implement xah-elisp-mode, even if I code

(add-to-list 'auto-mode-alist '("\\.el$" . xah-elisp-mode))

in my init.el, the previously visited buffers that are automatically 
opened when I start emacs will still be in elisp-mode. The fix, of 
course is to invoke xah-elisp-mode from the minibuffer. This is 
certainly doable, even with multiple elisp buffers opened, but I'm 
always looking to eliminate redundancies.

It would be handy if there were a command that would set all visited 
buffers ending in a specific file extension to a specific mode. If such 
were available, it would come in handy for experimenting with 
alternative major modes.

Is there such a feature?

Thanks

--

Tim

tj49.com