It sounds like you’re referring to a classic piece of RollerCoaster Tycoon 3 community history. The "no-CD patch" (or cracked executable) was a staple for players in the mid-2000s who wanted to avoid swapping discs—especially for the Platinum/ Gold editions.
Would you like a mock blog-post outline on this topic, or help finding a legitimate modern fix? rct3 no cd patch