If you extract the loose script files to your data folder, either from the bsa or from the loose files archive from the file mirror, you can change the summons to whatever NPC you want. Once you have the scripts and source in your folder, start up the CK with CaN as a master. The magic effects you'll want to change are aaaTommyDogSummonedEffect, aaaTommyDragonSummonedEffect, aaaTommyHorseSummonedEffect, and aaaTommyPonySummonedEffect. All you have to do is change the aaaCaNSummonNPC property to your desired NPC, then save your plugin.