When I looked for a way to have a character gain a ratfolk's swarming racial ability, the only method I was able to find was the mythic feat Mythic Racial heritage.
I'm not sure if it really works for what you have in mind, but its the closest I've seen to doing what you're asking. Short of making a custom race that is.
Sadly it doesn't work as Yaddithians are not humanoid.
I've long wanted to get Cosmic Mind without playing a Yaddithian. That is a seriously awesome ability. :)
ah, yeah I missed that they are Aberrations.
Also, for some reason my link above isn't working. Here it is for anyone that cares.
The arcmage mythic path ability Perfect Preparation does something similar to cosmic mind.