Can the Emacs 29 changes to the behaviour of defvar be reverted to its current behaviour?

According to some post I read the behaviour of `defvar` has been changed in that it will set the value of an already set variable if the variable is used again in a `defvar`. I use `defvar` declarations in order not to get *assignment to free variable* errors and I wouldn't want the existing values to be reset. I can't find the exact post where I read this but if this is what I think it means it may cause me some problems. Can anyone clarify it?

My Emacs 29.0.60 does not have such a change. I wonder if you are thinking of the eval-last-sexp change in Emacs 28, which will re-evaluate defvar now (ex: C-x C-e will re-evaluate this).

I would expect (defvar foo) to still do nothing but serve as hint for byte-comp, and (defvar foo nil) to now overwrite the value of `foo` if it had been set before. Someone please correct me if this is wrong.

defvar does not overwrite foo if it has already been set. https://www.gnu.org/software/emacs/manual/html_node/elisp/Defining-Variables.html The exception from Emacs 28 forward seem to be with eval-last-sexp.

Alright, thanks that makes it clear.

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