Could have, but would they? Representatives to the Virginia Secession Convention promised tariffs as high as Virginia manufacturers wanted them to be.
Also, without the navigation acts in place in the US, they would have either built up their own shipping industry to handle those exports.
They could have done that before the rebellion as well. Why didn't they?
Also due to the lower tariff, importers would have brought their goods into Southern ports - especially New Orleans, and then shipped them up the Mississippi river and distributed them throughout the Midwest.
Where they would have the tariff applied the moment they crossed into the U.S. So where is the advantage of landing them in the South again? Especially if they were taxed by the South before going to the U.S.?
It was reported that Confederate tariffs were going to be around 10%.
That either revenue from these duties must be collected in the ports of the rebel states, or the ports must be closed to importations from abroad. If neither of these things be done, our revenue laws are substantially repealed, the sources which supply our treasury will be dried up. We shall have no money to carry on the government, the nation will become bankrupt before the next crop of corn is ripe....allow railroad iron to be entered at Savannah with the low duty of ten percent which is all that the Southern Confederacy think of laying on imported goods, and not an ounce more would be imported at New York. The Railways would be supplied from the southern ports." New York Evening Post March 12, 1861 article "What Shall be Done for a Revenue?"
Perhaps they reported the facts incorrectly, and you have the correct information?
They could have done that before the rebellion as well. Why didn't they?
You cannot explain something to someone who doesn't wish to understand it. This has been covered many times before. One reason is Washington DC subsidies for the existing packet trade in the United States.
Pretty difficult to break into a market when the other guy is getting a base sum of money that you won't have to carry your operations.
Where they would have the tariff applied the moment they crossed into the U.S.
Only if you have the means to collect it along every waterway or potential border crossing, which would have been effectively impossible, and the impracticality of which was also noted by Northern Newspapers.
a series of customs houses will be required on the vast inland border from the Atlantic to West Texas. Worse still, with no protective tariff, European goods will under-price Northern goods in Southern markets. Cotton for Northern mills will be charged an export tax. This will cripple the clothing industries and make British mills prosper. Finally, the great inland waterways, the Mississippi, the Missouri, and the Ohio Rivers, will be subject to Southern tolls." The Philadelphia Press 18 March 1861