John has posted while I was investigating this and his term "lowering" expresses what I think this essentially means. I would suggest "downward inclination".

I have been using Anexo I to Articles 30 (j), 31 and 32 of Argentina's Ley 24449 de Tránsito y Seguridad Vial. I think this may be the text you're dealing with, in fact; it includes your paragraph C.1.1.4.3.1.

Later on, paragraph C.1.1.4.5. talks about alignment of dipped headlights ("passing beam" in Euro-speak), and includes the following:

"Alineación vertical: La horizontal de la línea de corte del haz debe ser paralela a la horizontal de la pantalla y rebatida por debajo de la misma, según las especificaciones del fabricante. Este rebatimiento debe estar grabado en el faro principal o en una plaqueta adherida a la carrocería del vehículo.
El rabatimiento estará comprendido entre:
- UNO POR CIENTO (1 %) donde para CIEN MILIMETROS de la pantalla DIEZ METROS es igual a UNA CENTESIMA DE RADIAN (100 mm = 0,01 rad (34', 37) en la pantalla a 10 m).
- UNO CON CINCO POR CIENTO (1,5 %) donde para CIENTO CINCUENTA MILIMETROS de la pantalla a DIEZ METROS es igual a QUINCE MILESIMAS DE RADIAN. (150 mm = 0,015 1°,08) rad en la pantalla a 10 m)."
http://www.agvp.gov.ar/Educacion Vial/Ley de Transito/Anexos...

Now, I think the meaning can be clearly deduced from this: "rebatir" means lower. The upper limit of the cut-off or break line (línea de corte) must be below the horizontal line on the screen by a specified percentage or number of degrees. This British page on MOT testing of headlights has some useful illustrations:
https://mattersoftesting.blog.gov.uk/the-mot-headlamp-aim-te...

I think "downward inclination" for rebatimiento and "incline downwards" for rebatir would be suitable. See the UK Road Vehicles Lighting Regulations 1989:

4 (b) (i): "If the dipped-beam headlamp bears an approval mark or not and the headlamp can also be used as a main-beam headlamp its aim shall be set so that the centre of the mean-beam pattern is horizontal or inclined slightly below the horizontal"
12: "(b) Every vehicle which–
(i) is fitted with dipped-beam headlamps bearing an approval mark,
(ii) has a maximum speed exceeding 25 mph, and
(iii) is first used on or after 1st April 1991
shall be marked with a clearly legible and indelible marking, as illustrated in Schedule 23, close to either the headlamps or the manufacturer’s plate showing the setting recommended by the manufacturer for the downward inclination of the horizontal part of the cut-off of the beam pattern of the dipped-beam headlamps when the vehicle is at its kerbside weight and has a weight of 75 kg on the driver’s seat. That setting shall be a single figure–
(A) between 1 and 1.5 per cent if the height of the centre of the headlamp is not more than 850 mm above the ground, and
(B) between 1 and 2 per cent if the height of the centre of the headlamp is more than 850 mm above the ground."
http://www.legislation.gov.uk/uksi/1989/1796/schedule/4/made

The parallel with the Argentine regulations (between 1 and 1.5 percent) is really quite close.

By the way, I also looked at these EU regulations on headlights, which don't solve the problem of "rebatimiento" but may be useful for backup.
https://eur-lex.europa.eu/legal-content/EN-ES/TXT/?uri=CELEX...

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Note added at 5 hrs (2018-06-07 09:04:06 GMT)
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Cheers, Robert. I haven't looked up the US regulations, but the language is probably compatible. "Tilt" would be OK, as far as I can see. Like you, I went for "inclination" because I found it used in official documents.

"Rebatir" seems to be used in the sense of "retract" in some cases. I've seen references to "faros rebatibles" (those pop-up headlights that used to be considered really cool), and to "retrovisores externos con rebatimiento eléctrico", which must mean retractable wing mirrors. They also refer to "rebatir los asientos", meaning folding the rear seat backs down to make room to carry large items in the back of the car.