Having defeated New Zealand -- who thrashed England by eight wickets at Wellington in February en route to the World Cup final -- 3-2 in a thrilling one-day international series, Morgan's men inflicted a 56-run thrashing upon the Black Caps in Tuesday's tour-ending Twenty20 international at Old Trafford.
"This felt a million miles away after the World Cup," said Morgan of a global tournament where England suffered a humiliating first-round exit without beating a single rival Test nation.
"This is a fantastic way to finish what has been a great month of cricket," he added. "When you're trying to implement change within a group it's important to have successes along the way and these guys have had that.
"We've done it the way we said we would and that's important too. I want these guys to play with as much freedom as possible."
Man-of-the-match Joe Root top-scored with 68 in England's 191 for seven, but New Zealand were well-placed at 88 for two and requiring 104 off the last 12 overs for victory.
However, they suffered a batting collapse that saw their final five wickets lost for just four runs in 12 balls.
New Zealand were dismissed for 135, with Kane Williamson's typically elegant 57 a rare highlight.
England Twenty20 international debutants David Willey, who also ran out Williamson with a brilliant pick-up and throw from cover, and Mark Wood took three wickets apiece.
For England, who shared a two-match Test series 1-1 with New Zealand earlier in the season, it was an ideal way to sign off before they begin their bid to regain the Ashes from Australia next month.