The email subject from this morning seemed like a very late April Fools’ joke at first: “NASCAR Adds Fourth Stage to Coca-Cola 600.”

Oh no.

Look, I get what NASCAR and Charlotte Motor Speedway are trying to do here. The 600 is a long race, and dividing it into four 100-lap stages will break it up and make it more entertaining. Last year’s 600 was brutal — with 131 straight green-flag laps at one point — and people hated the race.

And the stages have added a lot to the racing this year, so an extra stage is fine. Honestly, I wouldn’t mind if all races had four stages next year.

But…ughhhhhh.

What NASCAR fails to understand (or at least value highly enough) is how bad it looks to change rules in the middle of a season. These are the type of temptations a sanctioning body should avoid, because they harm credibility — and that’s very difficult to earn back.

Personally, I’m still affected by the worst decision of all time — adding a 13th driver to a 12-driver playoff in 2013. NASCAR changed forever for me that day, and I can honestly say I’ve never looked at NASCAR as a sport quite the same after that.

The Coke 600 decision isn’t on that level, but the concept is similar: A short-term play could have a long-lasting impact on people who are desperately clinging to the notion NASCAR is more of a sport than sports entertainment.

Yes, the “pure sport” aspect has been gone for awhile now — I get that — but it’s painful to see NASCAR toss aside more of its credibility.

That’s what makes this the wrong move.

NASCAR announced stage lengths for every race on Feb. 16. It said each race would have the same amount of stage points and playoff points, except for the Daytona 500 (which had 10 more stage points — but not playoff points — thanks to the Duels).

Now — less than two weeks before the 600 — NASCAR has suddenly decided a certain race is worth more stage points than other races. And it’s worth more playoff points than any other race.

Think about that: Drivers can earn more playoff points in the Coke 600 than they can in the Daytona 500.

That’s very troubling for purposes of consistency. All races should pay the same amount of points. And if they don’t, NASCAR should announce that at the start of the season — not 13 days before the race.

It’s really disappointing NASCAR decided to do this. Want to add a fourth stage to one race for entertainment purposes? Then at least do it before the season. Announce it, let people digest it and come to terms with it.

But by doing it now, NASCAR misjudged what’s more valuable: One night at Charlotte or its credibility as a sanctioning body.