For one vessel nozzle I find that both WRC 297 and WRC 107 are applicable.
Can I model Nozzle as per WRC 297 in CAESAR II so that I can use flexibilities, so that nozzle loads will get reduce.
And after reducing loads, can I feed those loads in Application of WRC 107 in CAEASR II to check stresses as nozzle is applicable for WRC 297 and WRC 107?

"Yes" to your WRC107 questions.

The flexibility model is actually outside the scope of WRC297. Read this earlier post for details.

thanks