I believe those fields are used when you create a button on PayPal's site and then they are hosting it for you. At least the "hosted_button_id" is used for that and would provide no purpose for this plugin as it is not designed to use hosted buttons.
About the "cmd" field, it can be used to decide if the PayPal button is a donation button, buy button, subscribe button and so on. I guess you want to change that to use the plugin for something else than a donation button?
It would require to tweak the output code of the plugin. If you are comfortable with doing that you can locate the generate_html() function in the plugin and simply add an additional line within that function to set another value for the cmd.