Speaking to people from the future:
WeBWorK 2.10 should come with the ShowMeAnother feature (blogged about here: http://cmhugheswebwork.blogspot.com/2014/05/show-me-another-feature-for-webwork.html).
It can (alomst) be used to achieve the functionality that one gets with problemRandomization.pl. The problem-by-problem settings are stored in the database (and in .def files) just as one sets an attempt limit and a weight for each problem. The elements that are missing are control of when the button is available to students in relation to whether they have already gotten credit, and whether or not the due date has passed. But if it is of interest, we could add those.
For anyone adventurous enough to work on the develop branch, you could try using SMA earlier than 2.10.
Turning off problemRandomize for a single problem
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