It's very possible. But doing so requires tools and the know-how.

If the changes were done using a tool available on most casas (plugged in through the OBDII/DLC connector), then there will be no trace of it ever happening, unless if it was documented like when the speedo/odo gauge was replaced due to a technical problem. But if the modification was done by replacing the flash memory located inside the speedo/odo gauge assembly, there might be symptoms such as broken seals/locks, solder residue, etc.