I've searched and cannot find an answer. The short question I think is how to create a variable with the values 1-30 and assign these to items.
I will give a brief synopsis of the design if there are better ideas.
The study has 30 quiz items. In one condition 10 items are shown, but for each item the respondent can choose to replace it with two new items that viewed right then (these replacement items have slightly different alternatives, but this shouldn't create a problem). No item can appear twice. I can see this working either by the results of the randomization becoming embedded text, and then using that in the display logic of future blocks, or (I think more simply) creating embedded data that is the values 1 to 30, and then just using the display logic to say what to display. I also want also want to record how long respondents send on each item and if I remember Qualtrics correctly this means each item has its own block (I think this is because of the randomization). So, here is what it might conceptually look like.
create var 1-30, a vector of the 30 integers shuffled. I guess this could be 30 individual variables, but with those shuffled values. Assign these as attributes for each item (so the 16th item may get number 4). So if Shuffle30 is the variable, Shuffle30[16] might have the value 4.
show item with the attribute 1. If they choose to see two replacement items show those with attributes 2 and 3.
show item with the attribute 4. If they choose to see two replacement items show those with attributes 5 and 6.
repeat until
show item with the attribute 28. If they choose to see two replacement items show those with attributes 29 and 30.

Sorry if I missed the answer to this on the web page or in my searches. Dan