No, that is usually not possible. The key switches are most often in the middle (or near the middle) of the key and with a stabilizer bar. To be able to put two keys in the same space, you would have to modify the PCB a bit .. and in most cases also a metal plate.
Of all keyboards with Cherry switches, only on some programmable Point-Of-Sale keyboards and numeric keypads are there double-width keys that fit over two switches instead of one plus a stabilizer ... and these keys are often not used for the main typing area.
On keyboards that use a shaft over a PCB or a membrane, what you are looking for is more common. It is possible to do on the IBM buckling spring keyboards Model F, Model M and variations.