An air-to-air heat pump is just an air conditioner that can be put into "reverse". If you can find an amenable contractor, the coil in your existing exchanger can be mated to a heat pump and your thermostat changed. And that would be it, but most likely they will want to change the whole shebang.

As for leaving this as a legacy, how long did your A/C compressor last? The useful life is probably ten years, give or take. There's no reasonable expectation that a heat pump will last any longer.

When buying a heat pump, the contractor will generally give you as specification for "COP", not a "SEER". The green energy field is filled with misleading data, COP is a great example. COP is the "efficiency" of the system relative to the energy consumed. A COP of 4 would mean that it extracts four times more heat from the air than it consumes in power. BUT, and this is important, COP is often misleadingly quoted at "standard conditions," or 70F. It will decline as temperature goes down, meaning that it's not a single number, but rather a curve. Somewhere around zero, the heat pump will have a COP of 1, meaning that it extracts as much energy from the air as the electricity consumed. So when you are told that a heat pump can work "all the way down to ten below", it's true enough, but the COP will be so low that it would be cheaper to heat with a resistance coil.

For my own use in the cold Northeast, I considered and rejected conventional heat pumps, regardless of subsidies. I would still be reliant on supplemental heat for half the winter, so it's not at all clear that there would be any benefit except in the "shoulder months", when it's not that cold. The subsidies mostly go to the profits of the manufacturers and installers, no benefit to the homeowner after the hired help takes their cut.

I would install water-to-air geothermal, which is a different kettle of fish, but only if I was doing new construction. The cost of retrofitting a well field or loop is cost prohibitive, and very disruptive. I have to live here while they'd be tearing up my yard.

My advice in considering green energy projects is "mind the bullsh_t." As usual, we're going to get to the future and find that it's not what they promised.