Strange -- that page indicates the suggestion was applied, but when I try it, it doesn't work:
Configuring GHCi with the following packages:
Loaded GHCi configuration from /tmp/ghci10227/ghci-script
Prelude> :set prompt "> "
> :{
Prelude| 3
Prelude| :}
3
> :set prompt2 "> "
Some flags have not been recognized: prompt2, >
> :{
Prelude| 3
Prelude| :}
3
>