Do I need to inform immigration before heading to Laos and what should I do upon returning to Thailand?

I reported my address (TM30) on the 04th July. I'm heading to Vientiane, Laos for a tourist visa on the 05th August. Do I have to inform the immigration office before I go or not? Once I (or rather If i'm lucky enough to...) return, what do I need to do? Technically, the 90 day period ends on the 02nd of October (If I have my maths right-it's not my strongest asset lol) so do I (or my friend..who is the owner of the property) have to update my situation? I will still be living with him up until I leave and for the remainder of however long I will stay in Thailand. Any help will be appreciated. I'm rather confused by the whole thing.