3) Can training make one better at the color-word version of the Stroop interference test?

Yes. The Stroop test is, along with spaced repetition, one of the most confirmed and replicated tasks in all of psychology, so it would be deeply surprising if no one had come up with training to make you better at the Stroop test. (Heck, there's plenty of training available for IQ tests - like taking a bunch of IQ tests.)

I'd put a very high confidence on that, but as it happens, I don't have to since I recently saw discussion of one result on Stroop test and meditation:

. After training, subjects were tested on a variety of cognitive and personality tests, including associate learning, word fluency, depression, anxiety, locus of control, and of course Stroop. Results showed that the TM and MF groups together scored significantly higher on associate learning and word fluency than the no-training and relaxation-training groups. Perhaps most surprisingly, over a 36 month period, the survival rate for the TM and MF groups was significantly higher than for the relaxation and no-training groups (p<.00025). But more to the point, both TM and MF scored higher than MR and no-training on the Stroop task (p<.1; one-tailed test).

Or:

Incredibly, behavioral data showed that the standard stroop effect (again, a cost in reaction time when reading incongruent words relative to congruent words) was completely eliminated in terms of both reaction time and accuracy for both the experimental and control groups. [ERP analyses revealed decreased visual activity under suggestions , including suppression of early visual effects commonly known as the P100 and N100, while fMRI showed reductions in a variety of regions including anterior cingulate]. The bottom line, then, is that even strong suggestion is enough to accomplish some amount of deprogramming, as measured through the Stroop task.