Sounds like a good plan. You can also try mulching with acidic mulches like pine bark. Good luck!

Several of the newer (last 10 years or so) hydrangeas don't change color with the soil pH, they just bloom the color they bloom. So, not knowing the cultivars, yours MAY change color and bloom as you want or may bloom as they did last summer, hopefully with blooms on the non-bloomer. If you REALLY want blooms of a certain color, you may have to buy ones that stay that color whatever the soil pH.

If you have one of the old-fashioned hydrangeas that will change color with soil acidity, you can take a soil sample to the Johnston County Ag Dept and the soil will be analyzed for free. Adding sulphur is a good way to reduce soil pH.

For the hydrangeas that change color between pink and blue (not all do), it's aluminum that makes them blue. Aluminum is usually present in the soil but isn't readily available to the plant at higher pH, so that's why people talk about making the soil acid. The soil test will let you know where you stand on both fronts, and if it turns out you need both you can use aluminum sulfate.

They are 'endless summer'.

Endless Summer will change color depending on the soil acidity.

Add aluminum sulphate and any good azalea camelia fertilizer (I like Hollytone because it's mostly organic and slow release) if you want blue and lime will cause them to turn pink.