So, there is no official rituals, ceremonies or prayers that are involved with selecting a yidam?
The yidam that I mentioned which does not require initiation is Lama Tsongkhapa. However there are other yidams which requires initiation or blessings from a guru. For now, Rinpoche has mentioned many times that Lama Tsongkhapa is perfect for this time and age.
Please don't think of yidams as stepping stones or degree's for you to learn and then jump from one yidam to another. All yidams are buddha's , and are here to help you gain enlightenment. No yidam is better or more powerfull than another yidam. If you may one day have the merit to be close to a lama, he may recommend certain yidam practices for you , because your guru will know which yidam is suitable to combat your negative alfliction . But in the meantime , Lama Tsongkhapa guru yoga is best, you will improve , you will transform your mind to be better if done with the correct motivation. This is the best Lama Tsongkhapa website. Full of explanation and information ..http://migtsema.com/