This is a limitation of the or_other
option. I've filed an issue with the pyxform team at https://github.com/XLSForm/pyxform/issues/218 in case they have some ideas. My guess is that the best solution for you will be to manually create the other option so you can customize it to your heart's content.
Also, welcome to the ODK community. When you get a chance, please introduce yourself here!