Whether or not you should amend individual planting holes is really determined by your current soil conditions. Blueberries prefer a quite acidic and richly organic, moisture retentive soil so amending to some degree is often called for. My choice when planting a quantity of plants liking the same growing conditions - i.e., multiple blueberries - is to amend over the widest area you can manage. The entire planting bed rather than individual planting holes

But if your soil already has a fair degree of tilth and is loose, easy to dig and well draining, you can amend planting holes modestly, especially for a smaller woody like a blueberry. I'd still not recommend that practice for larger trees.

While the current accepted convention is to NOT amend individual planting holes, it was the common practice for decades and often without any detrimental issues. Unless you have heavy, poorly draining clay soil, I doubt your amending has caused any serious difficulties.

The soil around those plants is pretty hard, and has lots of rocks. They've been in the ground just a couple of days, so I suppose I could pop them out and try what you recommend. I'd rather avoid that if possible, because its probably harsh on the plants and a lot of work.

Or, I am wondering if I can just use shovel garden claw to till up the area near the ones already in the ground (staying away from their root balls) and prep a larger area for the next one.

Blueberries are somewhat different than other shrubs,in that they need like gardengal wrote,an acidic soil.Before Dr.Coville successfully cultivated the first plants,many people tried and they never survived.He believed that learning the bushes needing an acidic environment was probably the biggest discovery.
Peat moss will provide that soil that they can thrive in.Some people grow them in it only,but I use about a 60/40 mixture of Pine and or Fir bark mulch to Peat moss with good results and then add the mulch each year to the area around the plant. Brady

So people just fill the hole up with peat moss and original soil? I knew that they really like acidic soil, but I think I just amended with cheap compost, and figured that I would be OK with just giving them the special high-acid organic ferts in the spring or whenever.

Yes,and mix some Pine or Fir bark mulch like I do.
I saw a photo of a healthy Blueberry plant growing in a bale of Peat moss with the plastic wrap still on it,something that I'd probably not do myself though.
There is a grower in Florida,where the native soil is sugar sand and has to fill the holes with Peat moss and Pine bark fines and does quite well.
Fertilizers probably won't provide enough acidity in the long run,even Ammonium Sulfate which is an acidifying fertilizer.
Adding Sulfur can be effective,but can take up to a year to see results and can be difficult to manage and maintain.
It also depends on the irrigation water's pH and bicarbonate load.Usually city water is treated to make it more alkaline,so it won't corrode pipes,so some people add some kind of acid to bring the pH between 4 and 5 if rain water is not available. Brady

Fall Creek Nursery - one of the largest wholesale blueberry growers in the country (and the primary supplier for blueberries for sale in local nurseries and garden centers) - is located in Lowell, OR and is an excellent resource for growing blueberries in our climate. FWIW, this is a prime growing area for blueberries and they seem to thrive even when the soil is not highly acidified - just left to a more or less natural pH (~6.0-6.5). They do recommend fertilizing annually with an acid fertilizer - the same you would use on rhododendrons and azaleas or camellias.

I've attached a link to their growing tips for homeowners which addresses all the details of siting, amending, fertilizing, pruning, etc.

Here is a link that might be useful: Fall Creek Nursery - blueberry care

Thanks gardengal48 for the great blueberry website.

from Fall Creek: A fail-safe way to grow blueberries in almost any soil is to incorporate peat moss into the planting medium. For planting directly in the ground, work up a planting area approximately 2ý feet in diameter and 1 foot deep for each plant. Remove 1/3 to ý of the soil. Add an equal amount of pre-moistened peat moss and mix well. (One 4 cubic foot compressed bale will usually be sufficient for 4-5 plants.) For raised beds mix equal volumes peat moss with bark (not cedar or redwood), compost or planting mix.

When my dad moved his old blueberries about 5 years ago after his farm sold & he kept the house he had to quickly get the job done in April. He still had his tractor to haul his old vegetable garden topsoil, nearly composted wood chips from the arena, and well aged horse manure compost. He mixed it all together & planted them in nearly 2 feet of it. He mounded the entire area up, but now it's just a bit higher than surrounding.

Mulching with leaves and coffee grounds along with a bit of our rabbit's manure now and then his plants were doing well until this year when he didn't get as much fruit set. Could have been the late spring frosts, but he thinks he needs more nitrogen. More rabbit manure and a spring feeding compost mulch should do it. An old Costco carport covered with golf course netting keeps the birds out! He also gave each shrub it's own space planting them 5' - 6' apart, so he would be able to walk around each bush easily. He cautions me to not plant them too close. With his method he doesn't irrigate much. Those wood chips are amazing!

Hope that helps.

Blueberries are shrubs. They are also ACID LOVING shrubs like azalia, So you have to add some sulfur around them to acidify the soil and fertilizer with azalia/evergreen fertilizer.