Normal DIMM's have a SPD flash chip soldered to the board which identifies the ram/timing parameters for the firmware/OS. At least on phones, to save a penny they forgo this and frequently the RAM capacity is tied to the model via hardcoded tables in the firmware. It wouldn't surprise me if at least on some of these "laptop" devices with soldered on ram something similar isn't being done.
So, at a minimum your flashing new ram parms to a SPD, or hacking the device model number somewhere. AKA, even with a rework station its likely a lot more than just swapping the chips, if there is sufficient PC/etc linage you might be able to swap the SPD chip as well, otherwise its going to be more than a mechanical heat it up, clean the pads, and drop/heat the new chip.
A lot of Apple hardware is locked down nowadays via hardware identifiers and the T2 security chip; it’s likely the RAM modules are not replaceable by the user even if you had the skill to solder a BGA.