First of all, just to clarify: You don't add effects when recording on GarageBand. Audio signals are recorded "dry" as they come in from the audio interface. All the effects you add on your Track are Playback effects.
Now to your question. "Yes you can!"
What you see in the Library Window are so-called Patches. They are a snapshot of a collection of Plugins and their settings that you can load to your Track. GarageBand comes with a wide variety of Patches, but you can save your own User Patches. Make any changes on a Track and then click on the "Save..." Button at the bottom of the Library Window.
Your custom Patch will be saved in you user directory ~/Music/Audio Music Apps/Patches/
After you saved your first custom Patch, the Library will display the "User Patches" item, where you can access those Patches from inside GarageBand.
You can exchange this files (with the file extension .patch) in the Finder (move/copy files in and out of that folder) with other GarageBand users. Just place them in the correct folder. If you find Patches on the internet, just place them in that folder and they will show up in the Library under "User Patches" (maybe close/open the Library or restart GarageBand to refresh the display.
I explain all those procedures in my Graphically Enhanced Manual (GEM) "GarageBand X - How it Works"
Hope that helps
Edgar Rothermich
http://DingDingMusic.com/Manuals/
'I may receive some form of compensation, financial or otherwise, from my recommendation or link.'
