On the current 201, there are only 6 pattern slots. However the first slot, Thru, really isn’t a pattern. But Thru is essential to stop an arp pattern from playing so that you can play normally.
So, in essence, while you have six pattern slots, only five are usable if you want to stop a pattern from playing (without having to cycle power).
What if when a pattern is active, pressing shift and the key corresponding to the actively playing pattern, the 201 would go back into Thru mode?
So, pressing shift + any different pattern would switch patterns normally.
But shift + the actively playing pattern, stops the pattern.
This way we could pick up an extra (usable) pattern slot.
I know the answer is to edit mother.pd, but I’m not at this level of editing (yet). 
Cheers,
CmD