Hi phoenix
Remember milk works in a demand-supply method

So if you are trying ot wean and therefore decrease supply slowly i wouldnt be expressing on top as your body will continue to produce enough for the feeds and the expressing thus defeating the process of weaning.

However if you get very full then you can express a little just to make you comfortable (not the whole breast!) and leave it at that

With DD we weaned quickly - in 3 days..
ANd my supply dried up in 7 days

I got very lumpy and full obviously but i would do regular massage in the shower which would leak small amounts of milk to make me comfy - cold compresses etc.

I did express once as it was really painful but only enough to be comfy and that was it.

i didnt develop mastitis.