Since mammillaria has many tubercles, you can increase numbers as you like.Maybe I should get some of my mammillaria tubercles/pups grafted to pereskiopsis!
Pereskiopsis stock many not work for some species, which many not form any off-sets.
The attached photo is for your reference.
It is a grafted M. luethyi tubercle with off-sets. Off-sets were removed and rooted later.