Όπως and σαν are interchangeable in many cases, with σαν being the most commonly used one.
The difference is that σαν means like, όπως also means however.
They are interchangeable in cases like
Είσαι κόκκινος σαν/όπως μία ντομάτα - You're red like a tomato.
But not in cases like
Do it however you like - Κάνε το/ Κάντο όπως θέλεις. (Where όπως is actually used like however)
So, in other words, όπως could replace σαν in some cases, but the cases that σαν replaces όπως are really few, if not none.^.^
Thank you very much! I love how the moderators here are always answering questions! Keep the good work :D
Really. Thank you Dimitra! Your explanations are always so thorough and patient. It makes such a difference. Same for all of the moderators. Ευχαρίστουμε πολύ!
Aww, παρακαλώ ^.^ I'm glad to see that I've helped learners even the slightest bit. It means a lot to me, as it means a lot to all the other mods.
And of course,thank you for taking the Greek course in the first place. ^.^