I have my ATP written but it will expire next month. I don't want to spend $3k plus for multi ATP. I have access to single engine for cost of fuel. Can I take ATP single engine and later add ATP multi without doing another written?

Or let's say I apply for regional with Single Engine ATP. How would new ATP written rule(Aug 1st) affect me?

I ask because I heard a rumor that multi and single will have a different written soon.

It would be great if I can take ATP single and just add ATP multi at regional in the future or when I have extra $.

Thanks!