No, you can't apply for a visa remotely. If you want to go to Laos you must make an appointment and you will apply in person. If you want to apply through Vietnam then you must be in Vietnam to apply, same as Malaysia.
The last news I saw was that both Chiang Saen and Chiang Khong are now 1 night required in Laos. For a little while Chiang Saen was requiring 1 night while Chiang Khong required 2, but then Chiang Khong switched down to 1 night as well.
First, check with your immigration office to see what they will allow you to switch reasons for your extension.
If they are okay with it, the only way to do it is like this:
1) You must be on a work extension, not an original 90 day non-B VISA.
2) When your extension is coming up for the next annual extension, you do not apply for the extension based on work, instead you submit your application for an extension based on marriage.
You may also possibly be able to switch if you are going to stop working. You would still need to check with your immigration office on this as well. What you would do is get a letter from your work stating your last day of work and take it to the labor department to cancel your work permit. Then you take that same letter along with your cancelled work permit to immigration and cancel your work extension. At the same time you apply for an extension based on marriage. Some immigration offices might allow this and some might not, that's why you need to go there and check first.
Just because the embassy says something doesn't make it true. There are a lot of embassies with stuff on their websites that aren't actually policies in Thailand at all. The embassy only knows if you tell them.
then you didn't arrive on the 60 day tourist visa or 60 day visa exempt because Bangkok only allows you to apply for extension when you have 45 days or less left.