Adding the solution should not change the problems unless there's a call to the random number generator that precedes the problem set up, which from your description seems that it will not be the case.
So I think the short answer is "no problem." One can imagine a case where one might succeed in changing the parameters in students' problems by adding a solution, but they don't seem likely and it appears that you're avoiding them in any case.
add solution to a .pg file while set is open
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