OJS 2.4.3 should behave in the way you want -- i.e. once generated, DOIs are attached to articles and won't be re-generated based on a different DOI configuration.
Does the Scielo XML file contain DOIs? If not, that's your problem.
As for ALM and Facebook sharing, I'm not sure, but I can forward this post along to the developer who wrote the ALM stuff. Do you specifically mean the ALM plugin available here
Public Knowledge Project Team