I dunno if that's true tbh. Internal party selections are not of interest to most of the electorate. Plenty of shit candidates parachuted into Liverpool constituencies in the past - cf. Luciana Berger, Frank Field. Sure there's more but those two spring to mind.TBF I don't think that will matter; if they do impose someone (especially someone ridiculous) as the official LP candidate then the city will probably vote for someone who was banned from the contest instead, just to spite them.
I doubt the conditions exist right now for an independent socialist to run and win in Liverpool.