[Exim] Change message when maildir quota exceeded?

Hello,

I am using Exim 4.32 to deliver messages to maildirs that are accessed via
Courier-imap, with quotas enabled. Everything seems to be working fine, but
when the quota is exceeded mail is bounced with the following message...

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:
  save to /path/to/maildir
    generated by local_part@???
    mailbox is full

Is it possible to change this message to something like 'Destination mailbox is
full', hiding the actual path to the maildir?

For reference, here is the transport that delivers to the maildir...

local_maildir:
driver = appendfile
maildir_format
maildir_tag = ,S=$message_size
quota = ${lookup mysql{ select quota from EMAIL_BOX where
domain_name='${quote_mysql:$domain}' and
local_part='${quote_mysql:$local_part}'}{$value}{1K}}
quota_size_regex = S=(\d+)$
quota_warn_threshold = 80%
delivery_date_add
envelope_to_add
return_path_add
user = maildir
group = maildir
mode = 0660
directory_mode = 0770


thanks and regards,

Steve