I've just converted my tourist visa to a non '0' visa with a view to getting the one year extension based on retirement. I have to wait till mid April for the 60 days to elapse on the 800,000 in my bank account before applying for the extension. I need to go outside Thailand twice before that date and am aware that i can do this with 2 single re-entry permits. However i was thinking of getting a multiple re-entry to cover me for these and additionally for any trips i may make during the one year extension period. Is this possible or will i need to get a new permit when i receive the extension?

You will need a new one, re entry permits are dated with your current entry expiry date, not future.

Thanks. I thought maybe that would be the case. I'll get single ones until after i receive the extension.