Date Range Merge Codes to work on custom fields

Piggybacking off this Q&A:

https://support.americommerce.com/hc/en-us/community/posts/201387574-Date-Format-for-EMAIL-template

The new date merges ##ORDERDATE[yyyy]## (etc) works as expected for modifying dates, but the formatting still doesn't seem to work with custom fields (set to be date fields) unfortunately