Can you create a PO in Euro and pay in dollars?

Maybe. You can pay POs/Bills (and any doc I think) with a bank account whose currency matches the PO or one that matches the functional currency of the subsidiary the PO is on. So yes if you're putting this PO on a USD sub, no if not. Assuming that hasn't changed. I haven't been dealing with FX as much lately.

see SA 14257; it is still in effect I believe