Skanda Purana states:
Aasya madhya sthitha veda devadevasya bhasura? aksharam
tu dautam jihvayam tu Sivajnana
Vedas are the middle of the mouth, agamas are the tongue and the aksharas are the teeth of Lord Siva.
Every agama contains four parts: Kriya Pada (rituals, offerings, prana prasthita, etc.), Karya Pada (when/where bath should be taken, how to clean oneself, lifestyle practices), Yoga Pada and Jnana Pada.
Kamikagama is one of the longest Agamas and South Indian temples follow this. It deals with all the rituals from ground-breaking ceremony, installation, prana prasthita (in purva bhaga) and diksha, festivals in uttara bhaga. The total number of verses are around 12000: 5166 in purva and 6477 in uttara. See complete translation in
If the people who perform the puja daily and the people who visit the temple are "pure" and follow the yama/niyama properly, there is no need to perform prana prasthita again and again. But since people will not follow the rules, prana pratishtha is done during kumbha abhishekam (See 75th chapter) every 12 years. Based on Rig veda 9.86.3,
"the powers descend from heaven, flow, to the kalasha, with his thousand streams and rests in the idol where Mitra dwells"
Further every year, the acharya should perform homa etc. to ward off all evils, defilement and other inauspiciousness (see Chapter 21 of the above book).