It very much depends on what you mean by
mess up. For the purpose of this answer I will assume you meant engine damage linked to combustible type, rather than other possibly infrastructure-related issues.
This guy seems to have driven quite a few kilometres in South America, and can thus provide some useful hands-on experience. Probably worth a reading.
Understanding Octane Ratings
Fuel octane ratings indicate the likelihood of the fuel detonating when subject to compression. A higher-octane fuel is therefore capable of withstanding higher compressions than a lower-octane. Compression is an intrinsic phase of the correct operation of an internal combustion engine. Compression results in an increase of temperature, and can therefore cause low-octane fuel to ignite. However fuel ignition is a precisely-timed operation, in that the ignition should be commanded by the spark plug only, when the piston reaches a precise point in its stroke. Pre-ignition caused by spontaneous detonation can be harmful to the engine.
Mexico and USA Use Comparable Octane Ratings
Both the USA and Mexico display octane rating in Anti-Knock Index (
AKI), which means that the octane values you read on Mexican filling stations will be comparable to those back home. Mexican unleaded petrol comes in two octane ratings: 87
AKI and 92
AKI. Hence pick the rating that most closely resembles the one you normally use in the US and you should be safe.
Comparing Octane Ratings
In case you were to drive in countries that use an octane rating different than
AKI (usually this would be Research Octane Number
RON), you could use this very heplful conversion table from wikipedia, which states that:
AKI is ≃ 90/91/92
AKI is ≃ 95/96/97/98
Guatemala and Costa Rica, for example, seem indeed to use