Pre-filled input for readline()

Is there a way to pre-fill the buffer for readline()? Say for instance I want to have the following

Enter a name for this run:
20XX-MM-DD |

where the date is already filled in and a user’s cursor is at the |, that way they don’t have to enter the date for each run, and can delete it if they want to. Is this possible? I couldn’t find anything about it.

I have no idea how to do this, but the request seems very useful.

As a workaround, maybe there is a way to push the desired string into an IOBuffer, as readline() seems to keep some kind of history when we use the up and down arrows?