ryjobil The IDE is powered by Ace.js which includes a lot of customisable options - I will be looking to expose some more of them to the user in the future.
For now, if you open on the board the file ~/Bela/IDE/public/js/bundle.js, on line 1824 (_this.editor.session.setOption('useSoftTabs', false);) you should be able to switch false to true to use spaces rather than tabs. There are plenty of other options which can also be modified in the same way.
