That's basically it, switch modules and restart Mercury. I assume you already checked that the new ISP isn't blocking port 25 for outgoing messages and that there is a reasonable PTR record for the IP address.

When we changed ISP's the IP address they assigned us was blacklisted by numerous entities requiring that I run MercuryC instead of MercuryE.  I have one email recipient for which transcripts are needed so I want to switch back to MercuryE.  A blacklist check on MXToolbox shows all clear so it appears the blacklist problem is resolved.  I don't remember the procedure I followed when I switched to MercuryC so wish to confirm that it is as simple as disabling MercuryC and enabling MercuryE (configuration verification of course).