is it possible to have a css file to be used as a theme that is located in a folder outside the open stage control one (actually the same one where is my custom module and all the js files)
This way I will be able to completely decouple my project from OSC files and folders
Yes, you can write the absolute path to the css file in the theme option (you have to put quotes around the path if it contains spaces, as the option accepts multiple values separated by spaces).