I wish the OP well. People getting frustrated by the railway not delivering the service it is intended to, and then becoming interested in the complexities in its operation and consequently wanting to work in the field to, in a small way, help to provide a better service, is nothing new. Just as a sensible hiring manager won’t make an issue about hair colour, piercings or non-offensive tattoos, a sensible hiring manager won’t make an issue (within reason) about people’s past attitudes and actions so long as they can honestly recount their reasons for them and discuss those openly.
I would, however, make one observation. A guard (conductor, train manager, call it what you will) is a very visible role, travelling on a train, often alone, with a great many passengers. If something goes wrong, or if one of those passengers perceives that something goes wrong, no matter how trivial and how distant from your own work, it will be your fault. You’ll have to explain it, and deal with it. Just the same as TOC social media employees who see people posting unpleasant things about their employers, and consequently feel like it’s their fault. You’ll have to reconcile that yourself, and you’ll probably have to reconcile that to any employer as well. In many ways I applaud you for even considering doing that, it’s not something many people have the capacity to do. In very general terms though, I would just be concerned that it’s for the right reasons.
