As for its tangible effect, the society only regarded such people as exceedingly devout believers. It’s not like undead will crumble to dust by only touching them, just because you received that particular real baptism.
Incidentally royalty, important nobles and major merchants could receive that real baptism as well by donating a high amount of alms. It was a compromise between rich people wanting to be given dignity as believers and the church’s side wanting to obtain money. Of course, one shouldn’t say it like that.