The phrase "i hereunto set my hand" refers to what?

the purpose of the heading in the passage is to identify who is telling the story.

this excerpt is part of the book sugar changed the world (2010) written by marc aronson and marina budhos. as the book has been written by two people, the heading "marc" indicates that this specific excerpt is being narrated by aronson. in the fragment, marc describes his grandfather's story after hearing it from his cousin. however, there are other excerpts where budhos is the one that tells the story of her family.

aronson and budhos, who are husband and wife in real life, decided to write sugar changed the world when they found out how sugar, which had an important role in slavery and economy, changed their ancestors' lives.

i think the correct answer would be adjustments in life roles.  this causes for one to adjust or change totally his/her career or lifestyle since the present is not beneficial to the life role he is at. for instance, you became a mother you would of course stop going to malls and enjoying life outside. you would be staying at home taking care of your child.