As we are going to release a new chain base on the old state and we want to avoid the break changes as much as possible.
I'm personally not aware of any way of doing this. I mean yes you could change the code to achieve this. However, there is a lot of code that has the assumption
0 == genesis. So, you would need to change a lot of code probably. This lead me to the answer, no you can not set genesis to a different block number.