The first obvious question is if you verified with he business if they really need to keep the historical data, e.g. is there a regulatory need. Often there is a demand to keep historic data, but in the end it's never used. If there is an actual and valid need, you need to consider the cost. Maybe keeping the old instance for a period of time as historic records is an option.
In short: don't gets stuck in searching a (technical) solution without being clear on the actual (functional) demand and the willingness to pay for that.
There is no way to copy the table across and rename it, maybe with the support of ServiceNow, but that seems very complicated to me.
Having said that, there are multiple options, all involving some sort of export/import. You obviously cannot do an XML export/import since it needs to go in another table. Also keep in mind that the task table has references to other tables, so you need to decide how you want to handle that.
What I can think of now as export options:
- Split the export in multiple batches, e.g. on "updated by", or just sort on sys_id and make evenly sized batches. You can increase the export limit via properties.
- You can create a web service call from the old system to the new and "loop" through all the records and send them to the new system using web services
- You can use the mechanism described in the ServiceNow Docs: Importing from another ServiceNow instance, but you might still want to split in multiple batches.
