Description
Yes, you can assert the nConfig signal directly after terminating a Partial Reconfiguration process.
However, you should ensure that you toggle PR_CLK for an additional 20 clock cycles before asserting nConfig, to flush the PR_CONTROL_BLOCK and avoid lock up.
Resolution
This requirement is documented in the Design Planning for Partial Reconfiguration section of the Intel® Quartus® Prime Standard Edition User Guide.