Compost is likely to make the soil more acidic, although slowly. I use sulphur granules to lower the pH and lime to raise it (there are two types available here - Garden Lime and Dolomite Lime - I use Garden Lime, as I recall there being a good reason not to use Dolomite for my application - martagons - but can't find my notes on it at the moment). The key point is not to change the pH too quickly.
