I just got back from KL where I wanted to get a multi-entry non-Immigrant B visa but ended up with only a single entry. I was told this was because I had no work permit, but other people who had a similar position did not need one to get their visa. I need to get this changed immediately as I have toi leave Thailand in 3 weeks! I was told by the embassy person that I could go to the Immigration office in Chiang Mai to change the visa. What will I need to get this done? I have only heard nightmares about the Immigration office and want to be ready when I go. I'm frustrated. Thanks for any help or insight.

You cannot change your visa to a multiple one. You can only apply for an extension of stay for one year if you have a WP and all documents.

If you have to leave for a short time, ask for a re-entry permit to keep your permission to stay alive.