Can I “Convert to manufacturer barcode”, if that barcode is a Amazon FNSKU barcode from an old (non existing?) listing, from a separate seller account?

So I have thousands of units of a certain product from my old amazon account that was attacked by a shady competitor, and subsequently shut down.

A few years went by, and I finally got a 2nd account, and started from scratch (on a new, separate listing) selling the same product. (Note: I’m just trying to get rid of this inventory, I haven’t had luck moving it on ebay. Not going to keep selling it most likely after I get rid of it).

It’s a cheap product, and so the $0.55 labeling fee really eats into the profit margin (IIRC labeling used to be $0.20 a unit or so).

I saw the option for “Covert to use manufacturer barcode”, and I was thinking this could really improve my profit margin (right now I’m actually in the hole $1500 or so, from getting this listing up, running ads, amazon fees, etc).

Since the old units are labeled with the old Amazon FNSKU barcode stickers from my old (now defunct?) listing, from my other account (inactive for years) – could I do the “convert to manufacturer barcode”?

Or does that option not work if the units are already labeled with an Amazon FNSKU?

(Note: I’ve had no issues with Amazon putting the new FNSKU labels over the old ones, when paying the $0.55/unit labeling fee).