Replacing the self signed certificate in Exchange 2007

Many thanks in advance for those who take the time to respond!

I have inherited an Exchange Server 2007 SP1 running on a Server 2003 SP2 x64 with the self signed certificate installed. Everything is functioning properly (Outlook, OWA, transport). We are looking to implement Active Sync so i know the self signed cert can not be used for this, or at least that is what i have read. The environment is a fialry straight forward one - Single domain, two DC's (one of which is running the cert services), single exchange server. Oh yeah we are also running BES, but i am pretty sure that is not affected by any of this. Here are my questions:

~By replacing the self signed cert with either one generated by a public CA or via the Windows Cert Auth what if anything wiill need to be done to ensure that OWA and still functions propoerly.
~ I have read mixed opinions on whether you should use a trusted third party CA or one generated in house via MS Cert Auth and was wondering, for this application (Active Sync), if there was a major difference
~ Once the self signed cert is replaced, if things go awry how do you re-assign the self signed cert (I can not seem to locate the cert via the Cert Auth MMC snap in.

I have searched the MS site and have found various articles related to the above, but none that explain how to re-assign the self signed cert if you need to.

Once again, i thank everyone who responds in advance with any assistance.