I need to create in certain circumstances, for different (up to 30) accounts, the same issue. XML Import will let me do this. What XML import does not do is: numbering these issues.

I now need a way to add the missing number once an issue is opened. Client Script onLoad seemed suitable. Yet I can't access that function .getNextObjNumberPadded()

As mentioned I tried everything. Could be, could not find documentation, this function is only available back-end. 

If this is the case, only available back-end, then I would need to know how. Business rules, I think, are only applied on Insert/submit, not on Import XML. Catalog Script I have no clue how to get that working, as again: I lack proper documenation