The proper tool costs less than $10 and will save at least that much in reduced aggravation and potential injury if the Atom freewheel is jammed.

I've been so broke it was a strain on the budget to spend $10 on a tool or essential component. But it was worthwhile.

And you can always sell or trade it later.

BTW, unless the Suntour is a must, you might consider a SunRace replacement freewheel. I've used them for a few years. Outstanding values. And they use the more standard Shimano splined tool. I have Suntour freewheels and the tool, in a box, just in case nostalgia strikes. But I prefer the SunRace freewheels.

Incidentally, when replacing a freewheel, after greasing the threads I don't crank down the freewheel tightly. I snug it down just a bit with the tool and my long wrench (a foot long or a bit more), then ride and let my body weight do the rest. Easy on an indoor trainer. Or do a lap around the parking lot, standing to pedal. Doesn't take much to snug down a freewheel securely but still easy to remove later.