How tall is it?
With ball-head attached it is slightly more than 12" The ball-head can be removed for packing and the legs are 9 1/2
Is it possible to replace the MT-33 ballhead with another one ?
Yes. I've done it with mine. The legs come with a 1/4 inch screw. It's not very long though and keep in mind this is a super light tripod so don't expect it to be able to handle a very heavy head + gear
After bending & wrapping the legs around something, is it difficult to make the legs perfectly straight again for level table-top use?
It is easy to straighten the legs back out. It doesn't wrap terribly tightly around things unless you bend it really hard, which feels like it will get broken at some point from that. Overall, it works wel and if it can get leverage on one leg against the others, it does hold position better.