How to match a filename only from the beginning

I'd like to match which only works if the match term is at the beginning of a filename (like in regexp: ^).
Use case: If a document is named 220816.mydocument.pdf, it should be rename to 2022-08-16.mydocument.pdf.
Unfortunately with the rule "Name matches date.filename and rename to date.filename.extension" with different date formats, documents like "Important docment draft - (220816).pdf" get renamed to 2022-08-16.).pdf.
Any ideas?
Use case: If a document is named 220816.mydocument.pdf, it should be rename to 2022-08-16.mydocument.pdf.
Unfortunately with the rule "Name matches date.filename and rename to date.filename.extension" with different date formats, documents like "Important docment draft - (220816).pdf" get renamed to 2022-08-16.).pdf.
Any ideas?