Warranty questions need to be asked against your brand's warranty documents -- there is not a 'general' answer.

My personal preference would be to go to a sheet metal shop doing a lot of stainless steel work (restaurant, usually) and getting sections of the thinnest gauge 304 they had cut to fit, and then pop riveting them into place with SS pop rivets. A shop like that will also have access to thin galvanized sheet.

Often pool wall sheet is too thin to sand, but you could put SS on top, and go.

Just be careful that you don't end up throwing good money away, fixing something that's almost gone. Check your support bases, especially. And keep in mind that you can buy a very functional 16 x 32 Intex AG for under $2,000