A UI control for global style changes overriding bootstrap defaults would be very helpful.
The program has 21 global Bootstrap themes built into it. After you create your new file, go to File > Design settings and you will see them in the drop-down menu. From here you can also import your own custom themes.
Google, "custom bootstrap theme generator" There are a number of free online websites where you can generate your own custom Bootstrap themes and then import them for future use.
Hope this helps.