How much is it changing the pH? How soft is your water? What kind of bogwood is it? Is it very hard, or rather soft and porous?
If hardwood, the less tannins it leaches the less effect on pH it should have. So in theory, you could simmer it until it doesn't stain the water very much, then put it in your tank. But the decomposition of the wood (however slight with hardwood) would still lower pH somewhat.
With the water changes you do, you should find that it maintains within probably .2 assuming you aren't getting pH bounce for other reasons.
CO2 will impact your pH far more than bogwood, as well as if your KH and GH are extremely low, you will get wider fluctuations. Even aeration could produce pH changes similar or even greater than what the bogwood might.
Using my tanks as a for instance, I have Malaysian driftwood in all the tanks. I change 25-30% of the water 2x/week. The pieces I have are quite dark, and do leach tannins into the water. The q-tank can get the color of a medium brewed cup of tea in one week. My water is quite soft, and I still only get a .4 drop in pH in that tank over the course of one week. Less if I do two water changes there.
Hope that helps.