I have done more research and am going to give what I now think is the answer to the original question here.

No, your blood ph is highly unlikely to change just because your urine ph changes. In fact, if it did you are not unlikely to be in a life threatening situation. HOWEVER...those little ph paper
readings are ultra important. Just because your blood doesn't match your urine reading, that doesn't mean lots of acid readings on those little ph papers is okey dokey. Just because you currently feel fine & dandy, though your ph papers say you have an acid diet (and they do report that correctly per research & my own experience) that doesn't mean everything is okey dokey.

For just one thing high acid readings in morning urine ph are associated with high blood pressure.

Below I have pasted a vid by someone I personally think is a bonafide expert. He has white hair. I like that in a health expert. Means he's had lots of experience. More importantly he is both an internist and someone much experienced with blood testing and nutrients, and ph levels, with thousands of patients.

He says we start out in life with reserves, biologically, and
high acidity may not bother us initially. The sad part is, we don't know when our reserves are running out until we maybe get sick.

Here's the vid. Hope it helps anyone.

http://www.youtube.com/watch?v=8fnfa48mjL8

He has other good vids too, on Youtube.

Regarding his very well researched protocol for Vitamin C, I would add this. If you "calibrate", per his protocol, for high levels of C and take mega sodium ascorbate you may find yourself becoming too alkaline. I found the answer to that was to find the right amount of ascorbic acid to blend in with the sodium ascorbate.

Btw a quick fix for acidity is to mix some lemon juice in with water and drink it. Apple cider vinegar might do the same thing. Drink with a straw to protect the teeth from the acidity.