You should simply swap out all instances of [b]&[/b] within the links and replace them with [b]&[/b] instead. A lot of affiliate-style links cause validation problems because of unescaped ampersands. It's not so much a modification to the code than a correction. The URL will work the same and it will validate properly.
Does it matter in terms of accessibility? You are required to have valid markup to claim a certain level of accessibility for your site. User agents however shouldn't have too many problems with unescaped ampersands as they are a common occurence on the web. It is always a good idea to fix them, however.