Dobrý den Vojta,
I would argue that Lines 1 and 2 of Guadalajara Metro are still light rails with some underground sections for the following reasons:
- They have sections that are overground and contain level crossings with car traffic. That alone usually is sufficient for the infrastructure to be not considered a subway in OSM
- The rolling stock TEG-90 and TEG-15 that is being used is not of a heavy metro but more of a heavy tram both in passenger capacity and speed
- Electrification is done via overhead wires instead of a third rail (not an exclusive argument against subway tagging, but subways are more likely to have third rail).
For more details on picking the right tagging see this section on the OSM wiki: https://wiki.openstreetmap.org/wiki/Tag:railway%3Dlight_rail#Recommendations

I would ask you to re-consider the tagging as a light rail to be in line with how this tagging is used in OSM and not have another local deviation.
I am happy to help reverting the tagging. Let me know if you want to take up the offer.

Best,
Claudius