In the field of physically-large CPUs I don't find this surprising. DEC 10's came in a wide range of models, and a KA10 variant for example could be field upgraded to a better variant, e.g. certain byte-access instructions added to extract bytes from 36-bit words, hardware floating point, and so on could be added. A technician would come and stick in some boards and wire-wrap them to the rest of the machine, and the machine's owner would pay for that. I only know of this with IBM and DEC but I would not be surprised if all the expensive machines were field-upgrade-able.