Generate static random numbers within formula

Why don't you try something like this

Set cell A1 to a toggle switch (ie you want the formula to update when A1 = YES) then change your formula to this

=if(A1="YES",IF(AND(B3="",C3="",D3=""),"",CONCATENATE("Student ",B3,"-",C3,"-",RANDBETWEEN(0,500000))),z1)

where Z1 is the cell reference you have this formula in. it will recalculate when you want it to (when A1 = Yes) and when you change A1 to anything but YES it will give you a circular reference warning the first time but only the first time but more importantly it won't change your number