Is it straightforward to alter a navbar so it could accommodate two lines of text per button?

I've done what I thought was the obvious, like adding <br> in the text, (as I've done with other programs), but the button text doesn't recognise it.

Would I have to disassemble a button and modify it, then reassemble afterwards, for example? I'm quite reluctant to do this as I'm still struggling to use some of the features.
Or is there an easier way?

I have a website at present that I want to re-design with WD11, it's an Xsite Pro website. In XSP I could put a second line of text in the buttons – you can see here: http://megalithmovers.org/