Updating OTA on openmode causes the packages to get updated, but any flashable parts (kernel, nolo, sw-cert) to not update. Thankfully, PR1.2's kernel is fully compatible with PR1.3, so NITDroid should still work fine for current users. If you reflash with PR1.3, you cannot use NITDroid until the PR1.3 sources are released. Since your device still identifies itself as PR1.2 (because sw-cert doesn't update), you could theoretically reflash with PR1.2 and ten re-upgrade OTA to PR1.3 if you need to do a reflash.
If this is confusing for you, DON'T UPDATE