Question about Den. aggregatum
 

I just got a Den. aggregatum in the mail from ebay. Plant looks very good, but it is planted in some very wet , old, Spaghnum . I would like to repot it, but since it's supposed to be going into dormancy, can I do it now or will it not grow new roots into the new medium ?

I would not repot unless it's in active growth. If it's not a tiny seedling, you're going to water it sparingly and let it dry out between waterings all winter, anyway.

You won't kill this one if you re-pot it at the wrong time but you might set it back. Like many other orchids, it is best to re-pot as new growth emerges.
I would carefully remove as much moss as you can (I have often used tweezers, chopsticks and wire to do this). If the orchid just falls out of the pot and the moss is easy to remove, I have found that if you set the entire thing on top of the medium and stake it well, usually the old roots won't die. When you see new growth on the roots, you can poke new medium gently around them. If the roots are clinging to the pot, leave it in the pot until you see new growth but keep out most of the medium. These guys don't mind being on the dry side (during dormancy--they like plenty of water otherwise. I have mine in a plastic Vanda basket with a little medium).
I have used this method with some orchids that hate re-potting and had success.

This is a very nice orchid. It blooms just once a year and the blooms last about seven days, not normally what I like in an orchid, but when it blooms, it is stunning. That is why this one has a firm place in my collection. :)

Just as a matter of curiosity, how do the pseudobulbs look and how is the overall health of the plant? I maybe over simplifying this, but I would think that if the pseudobulbs and roots are in good condition, you could hold off for a little while? like estacion seca said, you're just gonna water it sparingly and let it dry out anyway, lol :) best of luck, I hope it blooms profusely for you!

thanks all