Answering my own question: I just converted a prototype database with 20 tables using UUID() as keys. I did the following.
- add a new temporary column, called “temp”
- convert primary key column to “data colum” if not already done
- add trigger formula UUID and tick the field “Apply on record changes” and choose field “temp”
- goto column temp and enter “=1” into the first row - this triggers a record change for all rows and hence an automative update of UUID
- delete column temp - nice feature in Grist: the existing trigger point is set to “apply to new records”
PS: Thanks for the great work @dmitry-grist