I hold an APRC and have rented the same apartment for 5 years. My landlord hasn’t given me a contract the past 2 years and the last time he did my rent went up 
However, my GF moved in with me recently and I want to know how we can change her ARC address without a rental contract from my landlord? Can I take a cellphone bill with the address on it and write a letter saying she stays with me?
Also, am I required by law to have a consistent rental contract with my landlord?
Thanks!
I was able to change address to a relative’s home with a signed letter + id scan; mostly painless.
To change my address to my current location (rented under my girlfriend’s name), I had to bring a paper signed by her stating that I was living with her at that address and a copy of the rental agreement in her name.
(mod olm: removed off-topic stuff)
For ARC the address needs changed within 30 days of the fact of moving residence, first offense it an NT$2000 file. It used to be 15 days but I recall they updated it to 30 days which was the same for Gold Card holders (might need to check on that for a regular ARC).
I think this could be ok and you can sign an affidavit stating she lives with you from x date. Best to take the documents over to NIA and check, updating the address is free also.
You can buy a rental contract in 7-11, fill it out that you’re subletting to your girlfriend.