The customs declaration form has a "Equipo profesional de trabajo" (professional work equipment) line that most likely you should check, but there's nothing there that classifies this equipment as tax-free personal baggage if its value together with other items not classified as baggage is higher than the personal import allowance (500 USD).

You will probably need to make a temporal merchandise import to return to a foreign country in the same state ("importación temporal de mercancías para retornar al extranjero en el mismo estado"), meaning that the goods won't be transformed in Mexico due to repairs, upgrades, etc.

I think a customs broker would be your best option to make sure you can bring this into the country without having problems and taking risks. You might be legally required to hire a customs broker to process this; my guess is that the embassy will tell you to contact one.

I'm no customs expert but from what I understand from reading customs rules and regulations you should be prepared with at least this documentation:

- A letter stating the personal identifying information of the person who will use the equipment, where will the equipment be stored/used while in Mexico, a specific description of the equipment, a declaration stating a commitment to take the equipment out of Mexico within the time limit allowed by customs regulations, personal identifying information of the foreign resident (you).
- A letter from a resident in Mexico that declares that he'll be responsible for taking the equipment out of Mexico and for any taxes and fees that might result from the equipment not being taken out of the country within the time limit, as well as the personal identifying information of the resident in Mexico.
- A copy of the document (most likely a contract) that establishes the relationship between the resident in Mexico (who's hiring your services) and the foreign person (you), showing that relationship and that this relationship involves the equipment being temporarily imported.

References - Art. 106 Ley Aduanera and Section 4.2.2 Reglas Generales de Comercio Exterior