Yes you could but in practice one had to have a letter of marque to put them in use.
Unless you were a rich nut and liked sailing around armed to the teeth.
Use them without and you’d get hung for piracy.
One man’s pirate is another man’s privateer. At that time if you were wealthy enough to afford a warship you were also wealthy enough to get Britain, Spain ,France or the fledgling USA to rubber stamp your papers. Some privateers even switched sides with who would pay them more what a grand time to be alive except for the lack of antibiotics and air conditioning....
“Use them without and you’d get hung for piracy.”
Hanged.... it’s hanged. It’s a very important difference.
Merchant ships were armed for defense.