I have and use an XA often, in fact it's sitting alongside the keyboard waiting for me to finish and unload it's film and develop it this evening.
Basically you cannot override the meter easily, apart from changing the ASA rating. There is no way I know of to manually set a different shutter speed as well as a different F stop.
Basically, it is an aperture priority camera only.
That said, on the bottom you'll find a little lever switch. The first click out is noiseless and is called back light +1.5. This little feature is one of my most used parts of the camera.
The next part goes to Check, click this on and the camera emits a high pitched noise, this is teling you that the battery is alright.
The final switch is for the self timer, which is self explanatory once you use it.
I always use the camera with HP5+ rated at 320 ASA. In bright sunlight I sometimes find it a bit of a problem as the camera only goes to 1/500th of a second. I have two options, run the F stop to F22, sometimes even that isn't enough, or, switch the back light +1.5 lever into the on position.
Doing this, effectively drops the film speed to around 160 - 200 ASA depending on what you have set on your ASA dial. Yes you will get a slightly, to just more than slightly, over exposed neg, but at least it's printable, more importantly you had a little camera with you and you actually have the shot.
Mick.