You can create a chat file that is an executable script to be run automatically when the dial-up link is initiated. Thus, you can run additional commands during link initiation, such as stty for parity settings, besides the commands that are contained in a traditional chat script.
This executable chat script logs in to an old-style UNIX system that requires 7 bits with even parity. The system then changes to 8 bits with no parity when running PPP.
#!/bin/sh chat "" "AT&F1" OK "ATDT555-1212" CONNECT "\c" stty evenp chat ogin: pppuser ssword: "\q\U" % "exec pppd" stty -evenp