I want to lock my exam, not allow update from Library

Hi all
I use Library to generate exam (by ramdomized contents xblock). After the exam, I would to “freeze” the problems in exam as theye were at the time of examination, meanwhile the Library is updated day by day.

My question is, is there any way to lock the “ramdomized contents xblock” in an exam, not allow to update by new version of Library?

Thank you for your advice.