this sounds like with the new OS version there are new permissions on the folder.( verify with “ls -la”)
you can use chmod or chown to set the files to be able to be run by the user you are running the script as (this would be my suggestion). The easiest option for the file would be to use ‘chmod 777 /etc/dhcpcd.conf’ but don’t tell any linux people I suggested this, changing anything in /etc/ to 777 seems like a big security hole.
the other option could be to use ‘su’ and a username to run the script as a user who can already change the file permissions.