Comments by "Steve Valley" (@stevevalley7835) on "Guadalcanal Campaign - Operation Ke & Rennell Island, The Finale: (IJN 6(?) : 5 USN)" video.

@brendonbewersdorf986 There is just such a case, actually two. Germany sold two Brandenburg class pre-dreadnoughts to the Ottoman Empire in 1910. They served through a war with Italy, war with Greece and into WWI. The case more relevant to your hypothetical is when the US sold the two Mississippi class pre-dreadnoughts to Greece in 1914. Both of those ships were still in Greek service at the start of WWII: one as a gunnery training ship and the other disarmed, with the guns reinstalled as shore batteries. Both were riding at anchor at Salamis when attacked by Stukas and sunk in 1941. Based on the Greek example, I doubt pre-dreadnoughts, even if kept in something resembling combat condition, would have accomplished anything in the hands of any other country the Germans wanted to invade.
2
@brendonbewersdorf986 are you assuming the naval treaties exist, or not? We need to look at the precise language of the WNT, however, for some reason, the full text I have referred to in the past is not coming up in a search today. As I recall, the language of the treaty related the tonnage limits to replacement ships, implying that a power could retain more than it's quota worth of ships, but would have to start drawing down the surplus as new, replacement, ships were built. In the original treaty retention list, the RN was well over it's 525,000 ton limit. Even after the Nelsons were added, and four old ships eliminated in exchange, the RN was still over it's 525KT limit. If my read is correct, the US could have retained more older ships, if it wanted to, up to the moment it was granted authority to complete West Virginia and Colorado as replacements for the two Delawares, which would then compel adherence to the 525kt limit. If the US, in April 1917, had taken a page from the RN and cancelled all the Colorados and Tennessees outright, to clear the slipways for DD construction, then all the South Dakotas and Lexingtons are scrapped because they exceed treaty maximums, the USN would be stuck, not only with the Delawares, but also the South Carolinas and some of the pre-dreadnought Connecticuts to fill it's tonnage quota. Potential use for pre-dreadnoughts? Before US entry into WWI, it engaged in several "big stick" waving exercises, invading Haiti, the Dominican Republic and Mexico. As there was no opposing naval force, the USN used a variety of obsolete ships, battleships, armored cruisers and monitors, in those operations. In a post WWI environment, and a shortage of modern capital ships, I could see the US continuing to use pre-dreadnoughts in big stick waving exercises to frighten the locals. I doubt a Connecticut would be any deterrent to a Nelson though.
1