Since water can destroy Powder snow, you can abuse this, to make a snowy grass block stay in a World.

How to do?
https://www.youtube.com/watch?v=MQjQmhVmqUc&t=19s&ab_channel=Thunder
I have made a Video for this one! make sure to check it out. However, you would need some tries. I just got lucky on my 2nd. But, you can also do this a bit diffrent. Place 1 powder snow and a water on top of it! Then, click all around the water, until one of the bugs out and leaves a Snowy grass block. However, this is a harder way. Thanks!

Expected Result

The grass wouldn't stay in the snowy state