If you can do it in a way that doesn't duplicate a bunch of code then sure - but as I mentioned it'll still only work when installing (not when already installed).
If you'll then want to enable it so you can run whenever you want, I think you probably should have been making an interface.html all along :)
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
If you can do it in a way that doesn't duplicate a bunch of code then sure - but as I mentioned it'll still only work when installing (not when already installed).
If you'll then want to enable it so you can run whenever you want, I think you probably should have been making an interface.html all along :)