These are two different Puja, there is no doubt that Kaalsarp dosha is formed due to Rahu and ketu, however the puja and Mantras are different. For Kaalsarp dosha you will recite nag gayatri mantra and for Rahu you will recite the Beej mantra of Rahu.
Some even do the Maha mritunjaya Mantra for Kaalsarp dosha.
Blessings,
Navneet Khanna
Astrologer