The best way to assign divisi is with a spreadsheet.
At the top of the spreadsheet, List every divisi from standard voicing, with bar numbers and description.
For example: 6-part split, mm56-58
Immediately underneath that, list your standard voicing with all names.
Underneath that, list every divisi assignment
5-part split
6-part split
soprano divisi
alto divisi
Whatever you have, Title it, and then a column for each voice part.
You can use it to make sure you’ve divided appropriately. Ensemble members can use it to mark and double check their music. It works like a charm.