the universe patch is probably the easiest way.
There are also the season specific megapatches by elio
If you want to make your own MODs, then i would make a copy of your existing install (with the no-cd patch!!) and rename it to ie grandprixF1_2015.
Then remove all unnecessary jam folders, but keep liveries,main,genjam and techjam, both in gp3jams as gp3jamsh.
Install one of the latest gpxpatches
Install extra gpxpanels if you want, but this is not needed
use the car editor to load other carshapes (all in download section)
use gpedit to load the team art (all in download section and other gp3 sites)
download and install new tracks : check the download section! install instructions are mostly included
configure gpxpatch to load the tracks
replace the sound file in the samples folder for realistic engine sounds and atmosphere
If all goes well, you can can make your own MODs for every season, completely at your flavor
Modding can be so easy ..... or hard as you wish
good luck!