Station names should not be changed on signage or CIS or anything else similar. There are plenty of other opportunities, all rather more imaginative, to do themed things in stations, and enjoy occasions like this. It just doesn’t need any of the core signage to be changed.
Imagine if all the TOC and other journey planners / booking engines had ‘Brighton’ removed in the search list and replaced with ‘Frighton’, for one day only. Would you be able to plan journeys and buy tickets? Probably not, and nor would others. If it’s not acceptable there (it would be an RSP accreditation fail too!) then it definitely isn’t acceptable on trains / at stations either.