You would install them the same way you installed your local frequencies. It appears from the database that Troup County is on P25 digital. If your scanner cannot decode digital signals you will not be able to listen to them. Perhaps someone local can confirm if the GSP is using digital for this county.
Chances are, when GSP is working in Troup County, they will switch over to the Troup County talkgroup on the Muscogee race-to-waste system for running licenses and responding to local incidents but also have their VHF for GSP dispatch.
I have a Pro 106 and a Pro 197 I assume they will pick GSP up......I assume I can select add in ARC500? Also how do I add the NAC or do I have to? Also here in LaGrange we have a GSP Post.
In ARC 500 when you select the frequency the NAC will automatically be added to the SQ code column. The SQ mode column should have P25 in it but that also will be filled in when you add the frequency.