Plans change. Plants change. That shrub in the perfect spot 3 years ago is now in the worst spot you can imagine. So the question is: Will it kill it if you move it now? That depends on the plant.
But let's get one thing straight. The middle of summer is a lousy time for moving 99% of the plants in your yard. When it's 90 degrees and plants are growing actively, they need to pull lots of moisture from the ground with their roots and release it through their foliage. Disturbing their roots interferes with that and could mean a quick, crispy death.
So which plants can you maybe transplant now and which ones are doomed if you do? Here's a basic list. Keep in mind I'm talking about plants growing in the ground and not containers.
Trees. Just about none. Don't even try. You're bound to cut roots and that will cause transplanting shock. Wait until trees are dormant in fall.
Shrubs. The smaller the shrub is and the more compact its root system, the better its chances will be. You want to extract a root ball from the earth without the roots ever knowing it. Shrubs with leathery leaves taking moving better than those with large, soft, flexible leaves. So you can risk moving holly, boxwood, pittosporum, juniper, oleander, agave, yucca, or Indian hawthorn. Soak the ground around the plant the night before you dig, so the root ball will hold together. Important disclaimer: I'm not guaranteeing all these plants will survive. Nor are they the only ones you can try moving in summer. I mean, some plants like quince, loropetalum, and elaeagnus are just hard to kill. Just covering the basics here.
Perennials. Moving perennials in summer has a much higher success rate than tree or shrubs, because it's much easier to dig them without disturbing the roots. Again, wet down the soil the night before the move. Perennials I've successfully moved in the summer include daylily (even in bloom), bearded iris, sedum, black-eyed Susan, ornamental grasses, purple coneflower, Shasta daisy, penstemon, and summer phlox. If the plant flowers from a tuft of foliage (called a rosette) near the ground -- like black-eyed Susan, Shastas, phlox, penstemon, purple coneflower do) -- trim it down to the rosette before the move.
Bulbs. Spring-flowering bulbs like daffodils, tulips, and hyacinths are dormant now, so go ahead and move them if you want (if you can find them). They won't care. Don't move summer bulbs, like lilies, until their foliage dies down. Don't touch fall-bloomers until after they finish flowering.
Annuals. Do you really need to move your annuals? C'mon -- they're only going to be there for several more months. Let 'em be.