Q) why should not we apply tapta mudra by ourselves without permission of our kula gurus or other persons or sanyasis who are not our kula gurus?
A) If with out our kula guru's permission we apply tapta mudra by our selves we won't be getting siddhi, and also it will be a sin of burning sri hari the all-mighty and we'll be entering the hell for this wrong deed.

गुरुं विना तु यो दीक्षां स्वबुद्ध्या तु लभते नरः ।
न तत् सिद्धिं अवाप्नोति नरके चाभिपद्यते ।।१।।
तप्तमुद्रां तु यो मर्त्यः स्वबुद्धैव गुरुं विना ।
तेनाऽहं तापिते देवि नरके वसते ध्रुवम् ।।२।। (सदाचार दर्पणं)
these slokas of sadachara darpana explains us the above fact.

नरसिंहाचार्य सुळिभावि
मठाधिकारि,
गुंटूर, उत्तरादिमठम्
MOB-9493924608 ; 9490312275 visit my blog: HTTP://narasimhacharyasulibhavi.blogspot.com
to join my sms channel send sms as [ON] space [NARASIMHACHARYASULIBHAVI] to mobile number 9870807070
or http://labs.google.co.in/smschannels/subscribe/narasimhacharyasulibhavi go to this link online
you can see my prashnottara on uttaradimatham's official website uttaradimath.org in the category adhyatma jignyasa