My old way of redefining a command no longer works.

[Philip Taylor (Hellenic Institute)]

I suspect that what Steve meant is that his method has always worked for 
non-outer commands and this is the first time he has tried it with an 
outer ...

> Apart from the fact that \beginsection is declared \outer and therefore can't be used in a macro definition, no.
>
> I have texlive installations going back to 2015. In all that time, \beginsection has been \outer. If your redefinition used to work, you must recently have upgraded from a truly ancient version.
>
> – Harald
>