Implement correct toggle of non-default charsets chars like german Umlaute

[fsdafsadfsdsdaf]

Hi there,
is there any way to make toggle-rules work with non-default charsets chars like the german Umlaute?
There are upper case ÄÖU und lower case aöu. (well, technically there is also upper case ẞ and lower case ß, but the uppercase version is hardly used at all)

Can hashcat be told to include these mappings in the default toggle syntax? Would I have to manually edit the rules files or is it not possible at all?

Thank you.