Is there a way to import a list into Marketo that may have contacts that are already in SalesForce, without the list causing any problems with the individuals records in SalesForce?
I don't want it to overwrite the leads current information or history of interaction in SalesForce. If they are a hot lead I don't them all of sudden become a cold lead.
This shouldn't happen unless you are overwriting the specific fields that control these definitions, OR there is a smart campaign within Marketo that updates those values upon a change that you incite by importing.
Have you had this issue before when importing lists?
Understanding how you can block field updates is a good start: Block Updates to a Field - Marketo Docs - Product Documentation