I've done that, and it can work great. It takes a third channel and a console with polarity switches on the channels. Mics with a bi-polar pattern are a little harder to find.Am I the only one that mics a piano with a mid-side rig? Either the Schoeps or Neumann variety preferably? Live, but especially recorded on Grands that's my go to for anything more than closed lid.
The other thing to mention here is mono compatibility. If stereo isn't needed, one well chosen, well placed mic might sound better. A pair of widely spaced mics can have phasing issue. A pair does give you more controls over the blend of lows and highs. Mid-side and X-Y provide stereo with good mono compatibility,
Lately, I've been using an Avantone CK-40 stereo mic on a 110 year old Steinway. I think it sounds good in X-Y, placed in the crook. It does mid-side but I haven't tried it on piano. I have had issues with loose screws in the Avantone, so the Chinese build quality isn't perfect, but the price is nice. (Tightening screws holding the top capsule in is major surgery to reach.) Other than the screws, the component quality looks good.
I'm also tempted to try some Warm Audio recreations of vintage, classic mics. They seem to take pains at faithful reproductions and reviewers say they compare well to the real thing. A pair of their WA-84 (Neumann KM84) or WA-14 (early AKG C414) might be great on piano.