Can you easily change the A records to point to an IIS server through cPanel/WHM ?

There are two ways you can change the A records in the WHM interface.

First, you could edit the DNS zone manually and change the A records for the domain. To do this in WHM, you would scroll down on the left side of the screen to DNS Functions. Under DNS Functions, click Edit DNS Zone. From here, you can follow the directions on the right side of the screen.

OR:

You could change the way DNS zones are created so they use A records pointed to another server. To do this in WHM, you would scroll down on the left side of the screen to DNS Functions. Under DNS Functions click Edit Zone Templates. On the right side of the screen click the link that says Standard.

Here, you can change any of the following lines as needed for A entries:

%nameserverentry%. IN A %nameservera%

%nameserverentry2%. IN A %nameservera2%

%nameserverentry3%. IN A %nameservera3%

%nameserverentry4%. IN A %nameservera4%

%domain%. IN A %ip%

localhost.%domain%. IN A 127.0.0.1

The %domain% tag outputs your domain name. The %nameserverentry% tags output the names of your nameservers. The %nameservera% tags output the IP addresses of your nameservers.