[otrs] change ticketing numbering

We have two ticket systems running currently and in certain cases they send mail to each other. The problem we have is that tickets are being merged together that shouldn't be due to the numbering in the subject. For example first otrs system had a ticket 1, then second otrs system sends a ticket to it also with ticket 1 number, now there merged but two totally different issues. Can we change the ticket numbering to make one system unique. so instead of Ticket#2012060110000065, maybe Ticket#2012060110000065a. then both systems could not get tickets confused with one another. thanks Neil