It should be fine...it might not grow quite as much this spring as it would have had it been left in the old pot. However, in my experience the second summer growth will be larger after spring repotting because the roots have started filling in the new space you've provided them. So as long as you didn't disturb the root ball too much it should be fine.

I think it would be fine to repot it, but I would wait until the new growth hardens off some. Plants in general are tender right after a growth flush, and if nothing else, you make break some of the new limbs. Plants grown in containers can be planted or repotted just about any time as long as you use proper precautions. Transplant during the cooler parts of the day, like early morning or late afternoon. Be careful not to disturb (break apart) the root ball while repotting. Water right away after repotting, and keep the tree in a shady spot for a while. I have planted and repotted Japanese maples many times during the growing season. Although it is best to do while they are dormant, it can be done at other times. Moving a plant that is in the ground is another issue, and I wouldn't do that unless the tree is dormant.

I have repotted my new aka shidare momiji about 3 weeks ago or so, and infact 2 times in one week as I was given wrong advice on soil and the glazed pot I used got rather hot under the sun. in fact the last move to its current container, I had to wash away most of the soil on the roots as the soil would have been quite different from the new mix and caused problems. now its in a large terra cotta pot with good draining mix soil. I'm pretty new to this, so I guess I would not advocate what I have done, but seems like after 2 weeks in shade the tree is back to its health and budding new leaves well. some pictures I took yesterday and today.. Here is a link that might be useful: my new aka shidare momiji

there has been alot written on container soil here ...your choice is probably not the best...I doubt it will adversly hurt it in the short run but may compact and not be the best in the long run...Fertilizing JM's should only happen in early spring and MG has fertilizer ...that being said CQ's are pretty hardy and probably won't be hurt...here's the link to the gospel on containes ...I might take this with a small grain of salt since you are only doing one plant but it may give you a idea on how to augment your CQ maybe this fall if you are up for repotting ..I think some of this is a bit clinical and over the top for most folks but a hybrid use of this info may be useful to almost all of us and the basic logic behind it is correct IMHO!!!...whether you want to follow it to the tee is your choice or as I said maybe hybridize the jist of it which is what I would do unless you really want to "do" containers ...not just one...David http://forums.gardenweb.com/forums/load/maple/msg112314383375.html?23