Since Sylvana Sand was supposed to have inspired Gaemon Palehair’s edicts, do you think that in Dorne wounded veterans are supported by their Lords ? Would such a practice have been viable & implementable in the medieval times ? Any precedents for such moves in our world?

That seems to be the case, according to the WOIAF:

“An example of the differing Dornish laws and attitudes due to the influence of the Rhoynar may be found, curiously, in the last days of the Dance of the Dragons. From Archmaester Gyldayn’s history concerning Gaemon Palehair’s brief reign.”

So it probably is the case that Dornish veterans have to be supported by their lords, or that “the poor be given bread and beer in times of famine,” since we definitely know that in Dorne it’s definitely the case that “girls [are] equal with boys in matter of inheritance.”

Now, specifically on the point about veterans and real-world medieval practice…it’s hard to say, and it depends on how systemic a practice we’re talking about, and how many veterans survive their wounds vis-a-vis the capacity of the state. It’s certainly true that the medieval Catholic Church ran huge networks of hospitals that were as much about providing people with food and shelter as any form of medical care. And sometimes, you did have monarchs who would go out of their way to care for their veterans – after the failure of the Spanish Armada, for example, Phillip II provided medical care to the 10,000 survivors in attempt to expiate God’s wrath. On the other hand, Elizabeth’s government coldly refused to care for the sailors who had helped to save England purely for financial reasons.