This is a simple thing but I just discovered that with a simple regex and find/replace in most editors, you can quickly add text to the end of every line.
For instance, if you want to add a , to every line, all you need is $:
Or if you want to replace whatever the last character then you can use .$ instead.
Of course, I use vscode-neovim so I just type :%s/$/,/ 😁