We use this term more often related to emulators. Main board of arcade games or computer’s firmware. Simply, it is one of computer file containing a copy of certain data from a read-only chip, usually from a video game cartridge. But this usually takes a lot of time and need special gear or hardware to establish and for few times only.ROM reading speed of course is much different than RAM speed this is why we do copy ROM content to RAM before the first use, later we read from RAM.ROM writing speed: for ROMs electrically modified, writing speed is always way slower than reading speed, sometimes need high voltage.I think that I gave you a comprehensive and good idea about what is ROM, now back to our first question: what are Games Roms?Well to answer that, you need to know what is ROM image or ROM file. Like diode matrix and mask ROM or “MROM”, which means that we cannot change it after being produced.Lately, ROM has been updated to enclose read-only memory in normal operation, but we can reprogram it other way.Erasable programmable read-only memory or we can call it (EPROM) and electrically erasable programmable read-only memory or we can also call it (EEPROM), maybe it is a bit understandable by its name which we can erase and reprogram it again. The main use of ROM is to store firmware, now you may be wondering “and what is firmware?” Let me answer you - firmware is kind of software that closely related to a specific hardware and needs updates frequently, that was the firmware short explanation now back to ROM again, as I said that the main use of it is to store firmware or application software in something called plug-in cartridges.Read only memory refers to hard wired memory. Most of the times it is impossible to modify the data of ROM without having advanced knowledges in the IT field. Not only for Nintendo, but for the publisher of the game being localized (if it isn't Nintendo). I can certainly see your reasoning on it having to be profitable. This may be why they've actually made changes to those more than anything else. N64 games being the most modern are also probably the easiest to alter because they probably have a lot more documentation and are easier to deal with in general because the game source likely still exists and can be recompiled.

If the source doesn't exist you are limited to making only small changes to avoid breaking it which can be art or string swaps that are the same length as those found in the game to avoid shifting addresses.

From there you run the risk of breaking it, or introducing emulation issues that need to be ironed out. It has been speculated that the source code for these games may not still exist or if it does you basically need someone to go in there and figure it out which takes a lot of time and effort especially since older code will not be nearly as nice as it is today in terms of readability.

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