It depends on each person, different circumstances and different laws of different places. There can be no one or exact answer to this.
deidra:
1- blood is thicker than water
This is the only sentence of orthodox people to make their point.
2- it's ok to change your mind and abandon an adopted child anytime
I can say for sure about this thing that the law of any country does not allow this. its human emotion which are manipulated by people , situation or anything Because of which he leaves his biological or adopted child . This is not only about the children, but also about the elderly, sometimes the elderly are abandoned.
deidra:
3- adoption means you enter the family but you will never have the same rights as a blood relative
Under the law, both biological and adopted child have same rights, no doubt about it. as i said before different cases have different results . i know many people who adopted child and treated that child very well. if i talk about my closed one has adopted a girl child even they have already a biological child, and the whole family treat that girl as princess. so Every person's situation is different, mentality is different.
deidra:
4- is it ok for you that an adopted child agrees to be registered again in his/her "blood' family register after his/her adopted parents died? yes/no, why?
I'm not sure about registering procedure their is any law or restriction to do that. what i know about that in my country after you reach adult age adopted child has right to search/find for their biological parents , even for this adopted parents can't stop them . and it allow them to choose with whom they want to live .
note : I'm not aware of Korean laws or society how work in this things .