Actually your mom might not need to reactivate the household registration. The National Immigration Agency told me that the key aspect of this part of this option for applying is that your parent had an active household registration at the time you were born overseas. So in my case I needed to provide them an authentic copy of my mom’s household registration (inactive), which shows it was active during the date I was born. My mom has already passed away, so I’m not sure if this condition is different for people whose parent is not deceased. While applying, I’ve found that there are lots of little details and requirements/requests that are not clearly defined in the law, but are necessary to prove things and process the paperwork.
It is definitely best to directly ask the immigration officials. I recommend going in person, and not over the phone (the people answering the phones have given my cousin conflicting information in the past).
You can read more about what my process was like here: Reasons for NWOHR getting TARC - #14 by tando
On another note, someone mentioned above:
The difficult part is actually finding a place that’s willing to let you register because 90% of all landlords won’t let you.
I believe there was recent legislation passed to address this in part for people renting which takes effect June 1:
However, if your parent(s) reside outside of Taiwan, I’m not sure they would fall under this category if they are not renting.