In case you did not perform the surgery yet...
I highly recommend you use something like ChipQuik SMD removal Alloy. Look on amazon to get a feeling of what is available.
I have had great success with this in the past!
The main advantage is that the chance of ruining the chip or the PCB are almost nil. Also, you do not need to remove the PCB from the instrument (as you would if you preheat) if you can access the pins with a soldering iron.
The alloy looks like regular solder, but melts at a very low temperature of under 200 degrees Fahrenheit (similar to Wood's metal, but not so toxic). By melting it with a regular soldering iron onto the current solder (use lots of flux, it does not wet as well as solder, and flood all the pins making a huge puddle), the resulting mixture stays molten at a very low temperature, and for quite long, allowing one ample time to safely remove the chip.
If you have an adjustable temperature soldering station you can do the whole thing with the station set to a temperature well below the melting point of normal solder. This will ensure that you have almost zero chance to damage anything. Make sure you clean all remains of it from the PCB, as you don't want the new soldered chip to have this mixture too. The ChipQuik website has clear instructions.
The only disadvantage is that this alloy is quite expensive from ChipQuik (though you do not need much for a single chip, making it very acceptable overall). I believe more reasonably priced alternatives also exist.
In fact, I have researched this years ago and figured out what the alloy must be and bought some small bars of it form a non electronics-related source. It was much cheaper than ChipQuik, works perfectly, but less convenient in a bar form than in the ChipQuik wire form. Unfortunately, I have not documented my findings, and forgot the exact generic name of the alloy.
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