Maybe not but it is hard to tell since you do not state the pH of this amended soil.

Just remember that the roots which absorb the soil minerals are only growing in the potting mix now and they will not immediately react to the changes.... it may take until Spring for the roots to grow into this amended soil. In the meantime, you may just see gradual changes. In other words, change will not occur quickly. It will take years.

You have not mentioned how you are monitoring the soil pH changes. Get a soil pH kit so you do not overdo it and so you can monitor things more accurately. If you acidify the soil too much (say readings below 5.0), the plant will not be able to absorb some minerals. Similar to what happens with iron chlorosis but it will happen with other minerals like pottasium, phosphorus, etc.

Do not exceed the label application directions on the aluminum sulfate as this can damage the small roots and make the process take longer still.

I haven't tested the soil. Mainly because I just bought The hydrangea, and havent filled in the hole in the ground yet. And I've only treated it once in the container. I followed the instructions exactly. I'm going to get a testing kit, but money is sort of tight right now. If it helps the soil is just miracle grow garden soil and composted horse bedding/manure. For eveyr two bags of garden soil theres a bag of the manure.

If there is something about your soil that keeps them pink, I wouldn't worry too much about acid overkill. There is something about our soil that keeps them pink also. I don't think oak leaf mold with aluminum sulfate will be too much. We have oak leaf mold, I pour aluminum sulfate around my plants like there is no tomorrow, lots more than 3 Tbs, 3 or so times a year. Have yet to see a blue one. Best I can get is a light lavender. If you have high alkaline soil, that acid leaches right back out pretty fast. I have seen blue ones at a house where they are planted fresh from the nursery underneath pines, but by the end of the summer they are pretty light lavender.

I use aluminum sulfate and also (pelletized) garden sulfur to get my blue blooms. This has worked to produce blue blooms despite being a foundation plant (lime leaching) and my extremely alkaline soil working against me. It has taken a couple season, but it works if you keep at it.

Your plan sounds reasonable to me.

If the pine trees have been there a long time, then it may be possible that the soil under them is already quite acidic. Pine needles are naturaly acidic and the ground under a pine tree, after being dumped on by acidic needles year after year is often times much more acidic than the surrounding soil. You may be lucky and not have to add much acidity to get your desired blue blooms. A soil pH check kit would certainly help. Otherwise you'll just have to wait and see what you get and adapt accordingly.

Fingers crossed for blue blooms!