Not much point in the case of MAX_REDIRECTS, it's just an arbitrary value for loop detection (in practice, no sane link should redirect more than twice, really) – I only named it to avoid a magic number.

MAX_PRELOAD arguably could be useful to alter if heap space is really tight – in practice even 20 preloaded articles are rarely reached though, as long as the configuration of the consuming side is sensible. I'll add an optional property anyway!