I have a customer who's ISP blocks port 25 to send email so I am trying to figure out a way to do it for him which is usually done with ensim by editing the sites mailertable file, but cpanel setups do not come with this.

Does anyone know how to change this on a per site basis without effecting other customers?

There is an option in WHM under the service manager link that will run another copy of Exim on port 26 just for this purpose.

Thank you! That was exactly what I was looking for.