Permissions of files in the nix store are always 555 or 444, and home-manager doesn’t provide the option to copy the files with different permissions (like nixos’ environment.etc does).
You could use activation snippets or a systemd oneshot service to run a copy operation, if you really needed specific permissions on a declaratively set-up file.
Apologies for the delayed reply, I missed the notifications somehow.
Thanks for the responses. Out of curiosity, is there a reason this is not currently implemented in home-manager or is it just not something people are asking for?