Hi. You cannot us URL parameters to make a specific question read-only. You could hide it, but not make it read-only. You may need to publish a new dashboard-specific version of your survey where some fields are read-only.
Do you have any suggestions on utilizing an expression in the readonly column? e.g. a select_one ('yes' or 'no') question becomes readonly after the survey question has been submitted with a 'yes' or 'no' answer?
I've actually done this before, and there's a simple workaround for it. Add a throwaway question in your XLS form that isn't tied to a field, call it "disable_editing" or something.
Then, in the field(s) you want to disable editing for, put the expression "${disable_editing} = 'true'" into the readonly column.
In your embed URL, just use the field URL parameter to set that field to "true".
...?field:disable_editing=true