Hi Jelena,
Having been part of the SAP Globalization Services in Brazil, I understand a little bit of that process.
A few comments:
1) Localization of SAP solutions to country-specific regulation is under the responsibility of an area call Globalization Services. You can find more info about what they do here:
http://service.sap.com/globalization
2) Typically, those country-specific requirements are discussed in much details on the local ASUG chapters (at least that's how we did it in Brazil). That's why it's usually hard to find material in English, but I'd say that your local IT/Biz people in Mexico should be regulars in their local ASUG meetings, specially if they have a specific chapter to discuss Localization matters.
3) I found out this note with more specifics about "SAT Anexo 24".
http://service.sap.com/sap/support/notes/2041490
Apparently SAP is still analyzing it.
Suggestion if you want to speed the analysis up: reach out to your commercial contact in SAP.
4) Regarding your statement about the time it takes for the analysis & delivery to take place.
As an SAP customer, you have all the right to complain about the service level you're getting, it's just that, having been on the other side of the table, I know some facts that sometimes may be taken for granted. For example, SAP do not have infinite maintenance resources. I do understand that all customers pay maintenance and need to have their demands addressed, but SAP does not have a bench of developers available for whenever a new demand appears. If there is a new demand, they need to estimate the efforts and accommodate it into the development resource planning.
5) From a legal perspective, there is a difference between Legal Change and New Legal Requirement. The latter, if differing too much from the initial purpose of the acquired software, might not necessarily be required by the Software provider to be fulfilled within the maintenance scope. I'm not saying that it's the case for this Mexican requirement, I'm just saying there is this possibility, generally.
My personal recommendation: get your local Mexico people to be closer to the SAP Mexico team. They are usually responsible to publish information about such local requirements and the SAP release plan.
Hope that helps.
Best,
Henrique.