Converting context-free grammar to Chomsky/Greibach Normal Form
You can convert a context-free grammar into Chomsky normal form or Greibach normal form in whatever way you wish (converting a grammar to a normal form means finding a grammar in the normal form which generates the same language as the original grammar). A given algorithm might require you first to remove lambda productions, or first to convert to Chomsky normal form. If using a specific algorithm, you have to follow whatever the algorithm prescribes.