Lory23: For changing damage level (coefficent) just edit the file damage.ini in the SETTINGS folder.
Canadian76: For using only 1 perf file (if that´s what you mean) open the gpxset.ini file (in the Data\GPxPatch folder) and edit it to something like this:
[PerfManager] Enable =1 Path =gpxpdata\2017.txt (or whatever the name of your perf file is)