Rename seem to work fine here:
10.AmigaOS4:> cd ram:
10.RAM Disk:> echo foo > foo
10.RAM Disk:> rename foo Transactions_of_the_Royal_Martian_Geographical_Society_The_Journal_Of_Victorian_Era_Roleplaying_Volume_One
10.RAM Disk:> list
Transactions_of_the_Royal_Martian_Geographical_Society_The_Journal_Of_Victorian_Era_Roleplaying_Volume_One 4 ----rwed Today 12:08:15
3 files - 4 bytes - 2 directories - 10 blocks used
10.RAM Disk:> rename Transactions_of_the_Royal_Martian_Geographical_Society_The_Journal_Of_Victorian_Era_Roleplaying_Volume_One foo
10.RAM Disk:> list
foo 4 ----rwed Today 12:08:15
3 files - 4 bytes - 2 directories - 10 blocks used
version rename full
Rename 53.4 (06/12/2015)
What filesystem did you download the file onto?