No. Price discrimination and locking hardware are not illegal.

Probably not.

Doing a RAM swap and then selling the resulting unit as if it were a Raspberry Pi of the higher RAM capacity might be construed as trademark infringement[0]. And in general it's fairly difficult to make arguments in antitrust cases that boil down to "yes, your honor, everything they're doing is within their rights but I don't like it".

[0] At the same time, the scammers could probably get away with this by putting "Upgraded to 16GB!" in the title of their eBay listings or whatever, in the same way that fraudulent storage devices are labeled as "upgraded" (read: lying about their capacity). That doesn't impact the antitrust analysis though.