The body tissue of an offset is harder than that of seedlings.
An offset of Aztekium is hard especially.
You need pressure onto the scion when you grafted a hard offset normally but I found you do not need any pressure for these scions if you used Pereskiopsis as the stock.
I grafted 7 of Aztekium hintonii offsets in October last year.
The success rate of the grafting will be lower than seedling but it will be high enough if you use more than 10 mm diameter.
The photo is 1 of them, 40 mm diameter currently.