Provide a way to opt out of included plugins

I want to bundle a library using tsup, where I'd like to embed css as a string and also minify it. This is possible but unnecessarily finnicky with the current setup, as the embedded postcss plugin wants to take care of css files already. I would like to have the possibility to opt out of using the postcss plugin (or any of the other embedded plugins, for that matter), such that my custom plugin can handle css files.