Wait until the fall and make certain you don't use the stem to rock the ball lose. Trim back some of the top growth after moving. Everyone will see it next year.

Here is a link that might be useful: Propagating Perennials

Personally, I would move it now. You'll have to water lots but I've had crepes die back too much from cold when I moved them in the fall. Moving now will give months to develop the roots.

I move crepes all summer and plant them all summer too and they're fine. I have several I might move today.

I have moved crepe myrtles a number of times. I always do it in late fall or winter. The larger ones seem to take a while to get over the shock of transplanting. Personally, I think it is too late to move it now unless you don't mind losing it. Most plants to not take well to moving once they have leafed out, unless container grown.

Why not just get another one to put where you want it and leave the first one where it is for your enjoyment? If you're in the raleigh area you can get very reasonable big ones at broadwell's.

I relocated 4 7 foot crepe myrtles after becoming more aware of my yard's specs. The trees were simply not getting enough sun. It was in mid-spring since I don't do heavy garden digging in summer. I had heavy clay, rock, and dry earth. I was actually quite cruel to mine- and they did just fine! By the time I dug the last one, I was so exhausted that I only had about 3 inches of root on the bottom of the tree. I was in that frame of mind that I was going to get the darned thing OUT of the ground- then realized I compromised the transplant. Anyway, I staked it since there was not enough rootball to hold it in place- and watered slowly over a period of 2 weeks. It bloomed beautifully 2 months later and has continued to fill out nicely. .

I have a crepe myrtle that is about 12' tall that I plan to move this fall. So in the next couple of weeks, I am going to root prune it. I'll drive a shovel in the ground all around it, where I'll want the root ball to be to cut the large roots. Doing this will force the tree to make a whole bunch of new feeder roots that will be within the root ball size I have selected. Then this fall I'll move it and water it well for the next year. The tree will survive beautifully because of the abundance of new feeder roots it's grown all summer.