Jana, the presence of your landlady (or power of attorney) is only needed the first time you move into your address.
When you travel abroad and come back TO THE SAME ADDRESS you should go to inmigration and UPDATE your existing TM30. The only things you need for that is your passport, your new TM6 and your TM30. That's all.
Thank you so much! This will be my first visit to the new/old office :D
Uhm... If I travel again (thinking in going out for Loi Kratong), when returning, should I update in 24 hours or can update in 2-3 days? I thought you should update in 24 hours every time you come back...
Going to Vientiane for my first ever ED at the end of October, I hope it will be without problem... I will bring the original paperwork. Will update here.