We do not have a copy of Porter's orders. We have a copy of Mercer's orders relieving him of command, and placing a Lieutenant in charge of a major war vessel. (A Lieutenant is two ranks below a captain in the military ranking system of that time.)
For some reason, Porter never chose to release the text of his orders, but he was quite verbose about all the other things he did. He did show them to the harbor master, if I recall properly, but we can only judge what is in them based on how he proceeded to carry them out.
Can you think of any particularly good reason why he would sail the ship deep into the Atlantic away from normal shipping and then work so very hard to disguise the ship as something else? And then sail it all the way to Florida under a British flag?
Why would he do that? What possible purpose could he have in going out of his way to make sure nobody saw the Powhatan going to Florida?
And why would he immediately try to attack the Confederate shore positions upon arrival, and only be dissuaded by Meigs placing his ship in the path of the Powhatan. Porter even says he thought seriously of ramming Meigs ship to prevent it from interfering with his mission.
What mission was so important that he would consider ramming another US Navy ship to get at the Confederates?
If he had secret orders signed by Abraham Lincoln, it does not seem to me that anything that Meigs would have done or said should have stopped Porter. Lincoln outranked Meigs.
Or Porter did not have any separate secret orders to start a war at Pensacola. If he would have had them, he would have shown them to Meigs. In the end, If that was Lincoln’s intent, Porter failed.