I always thought it was the opposite. I thought he used that pressure defense half way through the year and that is sparked the run and why he used that philosophy to start here.
He backed off of the pressure a few games into the conference schedule, but I don't think the switch in philosophy was material. The first few games they played in the Big 12 season that year were against extremely efficient offenses. Their schedule got softer in the middle of their conference slate, which coincided with their improved defensive performance. Once they hit the end of the schedule and played top-shelf offenses again they reverted to early form (which continued in the NCAA tournament, especially against an extremely efficient Michigan team). They lost their last four games, all against offenses that Pomeroy had in his top 11, while giving up an average of 1.28 points per possession. In their first two games vs. KU and ISU, which were three of their last four opponents, they gave up 1.23 which is more or less the same outcome.
The whole 'switched defenses and won' thing is a great narrative, but they really just did a better job of playing less talented opponents. They were a weird team, best in the country offensively but 155th on D, mostly because of personnel issues but also because they prioritized crashing the boards over getting back on defense and also did a horrid job of cleaning up the defensive glass, none of which changed when they implemented a new system.