From my speculation, rather than the memory card carrying a binary (e.g. control code) that provides extra functionality, it's far more likely that the welding

From my speculation, rather than the memory card carrying a binary (e.g. control code) that provides extra functionality, it's far more likely that the welding machine is inherently capable of working at a large range of frequencies, but the control software deliberately disallows these options without the SD card, which likely carries some serial# or decryption key. A more suitable analogy would be a console game with so-called DLC that is already present on the disc. Or classic Casio fx-82ES => fx-991ES hack (OT: My copy of 82ES happens to be rev. A which is trivially hackable; Casio responded by producing a rev. B that is harder to hack). I personally believe that at least modification of this sort for own use (i.e. not offering it as a service) should not be prosecuted. That is, if I own this awesome welding machine, it should be totally fine for me to reprogram it, regardless whether I changed only one bit or page in the Flash, or completely wrote code for it from scratch.